Implement standard eth2.0 API (#1569)

- Resolves #1550
- Resolves #824
- Resolves #825
- Resolves #1131
- Resolves #1411
- Resolves #1256
- Resolve #1177

- Includes the `ShufflingId` struct initially defined in #1492. That PR is now closed and the changes are included here, with significant bug fixes.
- Implement the https://github.com/ethereum/eth2.0-APIs in a new `http_api` crate using `warp`. This replaces the `rest_api` crate.
- Add a new `common/eth2` crate which provides a wrapper around `reqwest`, providing the HTTP client that is used by the validator client and for testing. This replaces the `common/remote_beacon_node` crate.
- Create a `http_metrics` crate which is a dedicated server for Prometheus metrics (they are no longer served on the same port as the REST API). We now have flags for `--metrics`, `--metrics-address`, etc.
- Allow the `subnet_id` to be an optional parameter for `VerifiedUnaggregatedAttestation::verify`. This means it does not need to be provided unnecessarily by the validator client.
- Move `fn map_attestation_committee` in `mod beacon_chain::attestation_verification` to a new `fn with_committee_cache` on the `BeaconChain` so the same cache can be used for obtaining validator duties.
- Add some other helpers to `BeaconChain` to assist with common API duties (e.g., `block_root_at_slot`, `head_beacon_block_root`).
- Change the `NaiveAggregationPool` so it can index attestations by `hash_tree_root(attestation.data)`. This is a requirement of the API.
- Add functions to `BeaconChainHarness` to allow it to create slashings and exits.
- Allow for `eth1::Eth1NetworkId` to go to/from a `String`.
- Add functions to the `OperationPool` to allow getting all objects in the pool.
- Add function to `BeaconState` to check if a committee cache is initialized.
- Fix bug where `seconds_per_eth1_block` was not transferring over from `YamlConfig` to `ChainSpec`.
- Add the `deposit_contract_address` to `YamlConfig` and `ChainSpec`. We needed to be able to return it in an API response.
- Change some uses of serde `serialize_with` and `deserialize_with` to a single use of `with` (code quality).
- Impl `Display` and `FromStr` for several BLS fields.
- Check for clock discrepancy when VC polls BN for sync state (with +/- 1 slot tolerance). This is not intended to be comprehensive, it was just easy to do.

- See #1434 for a per-endpoint overview.
- Seeking clarity here: https://github.com/ethereum/eth2.0-APIs/issues/75

- [x] Add docs for prom port to close #1256
- [x] Follow up on this #1177
- [x] ~~Follow up with #1424~~ Will fix in future PR.
- [x] Follow up with #1411
- [x] ~~Follow up with  #1260~~ Will fix in future PR.
- [x] Add quotes to all integers.
- [x] Remove `rest_types`
- [x] Address missing beacon block error. (#1629)
- [x] ~~Add tests for lighthouse/peers endpoints~~ Wontfix
- [x] ~~Follow up with validator status proposal~~ Tracked in #1434
- [x] Unify graffiti structs
- [x] ~~Start server when waiting for genesis?~~ Will fix in future PR.
- [x] TODO in http_api tests
- [x] Move lighthouse endpoints off /eth/v1
- [x] Update docs to link to standard

- ~~Blocked on #1586~~

Co-authored-by: Michael Sproul <michael@sigmaprime.io>

testing/simulator/src/local_network.rs

@@ -1,6 +1,7 @@
 use node_test_rig::{
-    environment::RuntimeContext, ClientConfig, LocalBeaconNode, LocalValidatorClient,
-    RemoteBeaconNode, ValidatorConfig, ValidatorFiles,
+    environment::RuntimeContext,
+    eth2::{types::StateId, BeaconNodeHttpClient},
+    ClientConfig, LocalBeaconNode, LocalValidatorClient, ValidatorConfig, ValidatorFiles,
 };
 use parking_lot::RwLock;
 use std::ops::Deref;
@@ -123,7 +124,7 @@ impl<E: EthSpec> LocalNetwork<E> {
                 .ok_or_else(|| format!("No beacon node for index {}", beacon_node))?;
             beacon_node
                 .client
-                .http_listen_addr()
+                .http_api_listen_addr()
                 .expect("Must have http started")
         };
 
@@ -140,7 +141,7 @@ impl<E: EthSpec> LocalNetwork<E> {
     }
 
     /// For all beacon nodes in `Self`, return a HTTP client to access each nodes HTTP API.
-    pub fn remote_nodes(&self) -> Result<Vec<RemoteBeaconNode<E>>, String> {
+    pub fn remote_nodes(&self) -> Result<Vec<BeaconNodeHttpClient>, String> {
         let beacon_nodes = self.beacon_nodes.read();
 
         beacon_nodes
@@ -154,11 +155,9 @@ impl<E: EthSpec> LocalNetwork<E> {
         let nodes = self.remote_nodes().expect("Failed to get remote nodes");
         let bootnode = nodes.first().expect("Should contain bootnode");
         bootnode
-            .http
-            .beacon()
-            .get_head()
+            .get_beacon_states_finality_checkpoints(StateId::Head)
             .await
             .map_err(|e| format!("Cannot get head: {:?}", e))
-            .map(|head| head.finalized_slot.epoch(E::slots_per_epoch()))
+            .map(|body| body.unwrap().data.finalized.epoch)
     }
 }