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/Cargo.toml

@@ -0,0 +1,18 @@
+[package]
+name = "beacon_node"
+version = "0.1.0"
+authors = ["Paul Hauner <paul@paulhauner.com>"]
+edition = "2018"
+
+[dependencies]
+grpcio = { version = "0.4", default-features = false, features = ["protobuf-codec"] }
+protobuf = "2.0.2"
+protos = { path = "../protos" }
+clap = "2.32.0"
+db = { path = "db" }
+dirs = "1.0.3"
+futures = "0.1.23"
+slog = "^2.2.3"
+slog-term = "^2.4.0"
+slog-async = "^2.3.0"
+tokio = "0.1"