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.

protos/src/services.proto

@@ -0,0 +1,46 @@
+// TODO: This setup requires that the BN (beacon node) holds the block in state
+// during the interval between the `GenerateProposalRequest` and the
+// `SubmitProposalRequest`.
+//
+// This is sub-optimal as if a validator client switches BN during this process
+// the block will be lost.
+//
+// This "stateful" method is being used presently because it's easier and
+// requires less maintainence as the `BeaconBlock` definition changes.
+
+syntax = "proto3";
+
+package ethereum.beacon.rpc.v1;
+
+service BeaconBlockService {
+    rpc ProduceBeaconBlock(ProduceBeaconBlockRequest) returns (ProduceBeaconBlockResponse);
+    rpc PublishBeaconBlock(PublishBeaconBlockRequest) returns (PublishBeaconBlockResponse);
+}
+
+message BeaconBlock {
+	uint64 slot = 1;
+	bytes block_root = 2;
+	bytes randao_reveal = 3;
+	bytes signature = 4;
+}
+
+// Validator requests an unsigned proposal.
+message ProduceBeaconBlockRequest {
+    uint64 slot = 1;
+}
+
+// Beacon node returns an unsigned proposal.
+message ProduceBeaconBlockResponse {
+    BeaconBlock block = 1;
+}
+
+// Validator submits a signed proposal.
+message PublishBeaconBlockRequest {
+    BeaconBlock block = 1;
+}
+
+// Beacon node indicates a sucessfully submitted proposal.
+message PublishBeaconBlockResponse {
+    bool success = 1;
+    bytes msg = 2;
+}