Implement VC API (#1657)

## Issue Addressed

NA

## Proposed Changes

- Implements a HTTP API for the validator client.
- Creates EIP-2335 keystores with an empty `description` field, instead of a missing `description` field. Adds option to set name.
- Be more graceful with setups without any validators (yet)
    - Remove an error log when there are no validators.
    - Create the `validator` dir if it doesn't exist.
- Allow building a `ValidatorDir` without a withdrawal keystore (required for the API method where we only post a voting keystore).
- Add optional `description` field to `validator_definitions.yml`

## TODO

- [x] Signature header, as per https://github.com/sigp/lighthouse/issues/1269#issuecomment-649879855
- [x] Return validator descriptions
- [x] Return deposit data
- [x] Respect the mnemonic offset
- [x] Check that mnemonic can derive returned keys
- [x] Be strict about non-localhost
- [x] Allow graceful start without any validators (+ create validator dir)
- [x] Docs final pass
- [x] Swap to EIP-2335 description field. 
- [x] Fix Zerioze TODO in VC api types.
- [x] Zeroize secp256k1 key

## Endpoints

- [x] `GET /lighthouse/version`
- [x] `GET /lighthouse/health`
- [x] `GET /lighthouse/validators` 
- [x] `POST /lighthouse/validators/hd`
- [x] `POST /lighthouse/validators/keystore`
- [x] `PATCH /lighthouse/validators/:validator_pubkey`
- [ ] ~~`POST /lighthouse/validators/:validator_pubkey/exit/:epoch`~~ Future works


## Additional Info

TBC

Cargo.lock

@@ -720,15 +720,13 @@ dependencies = [
 
 [[package]]
 name = "chrono"
-version = "0.4.18"
+version = "0.4.15"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "d021fddb7bd3e734370acfa4a83f34095571d8570c039f1420d77540f68d5772"
+checksum = "942f72db697d8767c22d46a598e01f2d3b475501ea43d0db4f16d90259182d0b"
 dependencies = [
- "libc",
  "num-integer",
  "num-traits",
  "time 0.1.44",
- "winapi 0.3.9",
 ]
 
 [[package]]
@@ -790,7 +788,7 @@ dependencies = [
  "sloggers",
  "slot_clock",
  "store",
- "time 0.2.22",
+ "time 0.2.21",
  "timer",
  "tokio 0.2.22",
  "toml",
@@ -1292,6 +1290,12 @@ dependencies = [
  "zeroize",
 ]
 
+[[package]]
+name = "doc-comment"
+version = "0.3.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "fea41bba32d969b513997752735605054bc0dfa92b4c56bf1189f2e174be7a10"
+
 [[package]]
 name = "dtoa"
 version = "0.4.6"
@@ -1469,16 +1473,22 @@ dependencies = [
 name = "eth2"
 version = "0.1.0"
 dependencies = [
+ "account_utils",
+ "bytes 0.5.6",
+ "eth2_keystore",
  "eth2_libp2p",
  "hex 0.4.2",
+ "libsecp256k1",
  "procinfo",
  "proto_array",
  "psutil",
  "reqwest",
+ "ring",
  "serde",
  "serde_json",
  "serde_utils",
  "types",
+ "zeroize",
 ]
 
 [[package]]
@@ -2157,9 +2167,9 @@ dependencies = [
 
 [[package]]
 name = "hashbrown"
-version = "0.9.1"
+version = "0.9.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "d7afe4a420e3fe79967a00898cc1f4db7c8a49a9333a29f8a4bd76a253d5cd04"
+checksum = "00d63df3d41950fb462ed38308eea019113ad1508da725bbedcd0fa5a85ef5f7"
 
 [[package]]
 name = "hashset_delay"
@@ -2543,7 +2553,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "55e2e4c765aa53a0424761bf9f41aa7a6ac1efa87238f59560640e27fca028f2"
 dependencies = [
  "autocfg 1.0.1",
- "hashbrown 0.9.1",
+ "hashbrown 0.9.0",
 ]
 
 [[package]]
@@ -3641,9 +3651,9 @@ checksum = "77af24da69f9d9341038eba93a073b1fdaaa1b788221b00a69bce9e762cb32de"
 
 [[package]]
 name = "openssl-src"
-version = "111.11.0+1.1.1h"
+version = "111.10.2+1.1.1g"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "380fe324132bea01f45239fadfec9343adb044615f29930d039bec1ae7b9fa5b"
+checksum = "a287fdb22e32b5b60624d4a5a7a02dbe82777f730ec0dbc42a0554326fef5a70"
 dependencies = [
  "cc",
 ]
@@ -3844,18 +3854,18 @@ dependencies = [
 
 [[package]]
 name = "pin-project"
-version = "0.4.24"
+version = "0.4.23"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f48fad7cfbff853437be7cf54d7b993af21f53be7f0988cbfe4a51535aa77205"
+checksum = "ca4433fff2ae79342e497d9f8ee990d174071408f28f726d6d83af93e58e48aa"
 dependencies = [
  "pin-project-internal",
 ]
 
 [[package]]
 name = "pin-project-internal"
-version = "0.4.24"
+version = "0.4.23"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "24c6d293bdd3ca5a1697997854c6cf7855e43fb6a0ba1c47af57a5bcafd158ae"
+checksum = "2c0e815c3ee9a031fdf5af21c10aa17c573c9c6a566328d99e3936c34e36461f"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -3864,9 +3874,9 @@ dependencies = [
 
 [[package]]
 name = "pin-project-lite"
-version = "0.1.9"
+version = "0.1.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "4fe74897791e156a0cd8cce0db31b9b2198e67877316bf3086c3acd187f719f0"
+checksum = "282adbf10f2698a7a77f8e983a74b2d18176c19a7fd32a45446139ae7b02b715"
 
 [[package]]
 name = "pin-utils"
@@ -3956,9 +3966,9 @@ checksum = "eba180dafb9038b050a4c280019bbedf9f2467b61e5d892dcad585bb57aadc5a"
 
 [[package]]
 name = "proc-macro2"
-version = "1.0.23"
+version = "1.0.21"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "51ef7cd2518ead700af67bf9d1a658d90b6037d77110fd9c0445429d0ba1c6c9"
+checksum = "36e28516df94f3dd551a587da5357459d9b36d945a7c37c3557928c1c2ff2a2c"
 dependencies = [
  "unicode-xid",
 ]
@@ -4060,9 +4070,9 @@ checksum = "cb14183cc7f213ee2410067e1ceeadba2a7478a59432ff0747a335202798b1e2"
 
 [[package]]
 name = "psutil"
-version = "3.2.0"
+version = "3.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "7cdb732329774b8765346796abd1e896e9b3c86aae7f135bb1dda98c2c460f55"
+checksum = "094d0f0f32f77f62cd7d137d9b9599ef257d5c1323b36b25746679de2806f547"
 dependencies = [
  "cfg-if",
  "darwin-libproc",
@@ -4073,7 +4083,7 @@ dependencies = [
  "num_cpus",
  "once_cell",
  "platforms",
- "thiserror",
+ "snafu",
  "unescape",
 ]
 
@@ -5066,6 +5076,27 @@ version = "1.4.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "fbee7696b84bbf3d89a1c2eccff0850e3047ed46bfcd2e92c29a2d074d57e252"
 
+[[package]]
+name = "snafu"
+version = "0.6.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9c4e6046e4691afe918fd1b603fd6e515bcda5388a1092a9edbada307d159f09"
+dependencies = [
+ "doc-comment",
+ "snafu-derive",
+]
+
+[[package]]
+name = "snafu-derive"
+version = "0.6.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7073448732a89f2f3e6581989106067f403d378faeafb4a50812eb814170d3e5"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
 [[package]]
 name = "snap"
 version = "1.0.1"
@@ -5297,9 +5328,9 @@ dependencies = [
 
 [[package]]
 name = "syn"
-version = "1.0.42"
+version = "1.0.41"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "9c51d92969d209b54a98397e1b91c8ae82d8c87a7bb87df0b29aa2ad81454228"
+checksum = "6690e3e9f692504b941dc6c3b188fd28df054f7fb8469ab40680df52fdcc842b"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -5441,9 +5472,9 @@ dependencies = [
 
 [[package]]
 name = "time"
-version = "0.2.22"
+version = "0.2.21"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "55b7151c9065e80917fbf285d9a5d1432f60db41d170ccafc749a136b41a93af"
+checksum = "2c2e31fb28e2a9f01f5ed6901b066c1ba2333c04b64dc61254142bafcb3feb2c"
 dependencies = [
  "const_fn",
  "libc",
@@ -5456,9 +5487,9 @@ dependencies = [
 
 [[package]]
 name = "time-macros"
-version = "0.1.1"
+version = "0.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "957e9c6e26f12cb6d0dd7fc776bb67a706312e7299aed74c8dd5b17ebb27e2f1"
+checksum = "9ae9b6e9f095bc105e183e3cd493d72579be3181ad4004fceb01adbe9eecab2d"
 dependencies = [
  "proc-macro-hack",
  "time-macros-impl",
@@ -5891,21 +5922,20 @@ checksum = "e987b6bf443f4b5b3b6f38704195592cca41c5bb7aedd3c3693c7081f8289860"
 
 [[package]]
 name = "tracing"
-version = "0.1.21"
+version = "0.1.19"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "b0987850db3733619253fe60e17cb59b82d37c7e6c0236bb81e4d6b87c879f27"
+checksum = "6d79ca061b032d6ce30c660fded31189ca0b9922bf483cd70759f13a2d86786c"
 dependencies = [
  "cfg-if",
  "log 0.4.11",
- "pin-project-lite",
  "tracing-core",
 ]
 
 [[package]]
 name = "tracing-core"
-version = "0.1.17"
+version = "0.1.16"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f50de3927f93d202783f4513cda820ab47ef17f624b03c096e86ef00c67e6b5f"
+checksum = "5bcf46c1f1f06aeea2d6b81f3c863d0930a596c86ad1920d4e5bad6dd1d7119a"
 dependencies = [
  "lazy_static",
 ]
@@ -6236,13 +6266,19 @@ dependencies = [
  "exit-future",
  "futures 0.3.5",
  "hex 0.4.2",
+ "hyper 0.13.8",
  "libc",
+ "libsecp256k1",
+ "lighthouse_version",
  "logging",
  "parking_lot 0.11.0",
+ "rand 0.7.3",
  "rayon",
+ "ring",
  "serde",
  "serde_derive",
  "serde_json",
+ "serde_utils",
  "serde_yaml",
  "slashing_protection",
  "slog",
@@ -6250,10 +6286,13 @@ dependencies = [
  "slog-term",
  "slot_clock",
  "tempdir",
+ "tempfile",
  "tokio 0.2.22",
  "tree_hash",
  "types",
  "validator_dir",
+ "warp",
+ "warp_utils",
 ]
 
 [[package]]
@@ -6369,7 +6408,9 @@ dependencies = [
  "beacon_chain",
  "eth2",
  "safe_arith",
+ "serde",
  "state_processing",
+ "tokio 0.2.22",
  "types",
  "warp",
 ]