Add validator_node, restructure binaries, gRPC.

This is a massive commit which restructures the workspace, adds a very
basic, untested, validator client and some very basic, non-functioning
gRPC endpoints to the beacon-node.

beacon_node/db/Cargo.toml

@@ -0,0 +1,13 @@
+[package]
+name = "db"
+version = "0.1.0"
+authors = ["Paul Hauner <paul@paulhauner.com>"]
+edition = "2018"
+
+[dependencies]
+blake2-rfc = "0.2.18"
+bls = { path = "../../beacon_chain/utils/bls" }
+bytes = "0.4.10"
+rocksdb = "0.10.1"
+ssz = { path = "../../beacon_chain/utils/ssz" }
+types = { path = "../../beacon_chain/types" }