Replace kRPC

[ciera]

We should replace kRPC with gRPC. This will allow us to remove more kythe code from third-party.

[ciera]

Increasing priority; if we're going to change the protocol we should do it before more external analyzers get written.

[ciera]

We have several steps to making this work.

1. Fix up our third party repo and the build rules around them. It's a mess right now. We should use kythe as an example.
2. Add in grpc by setting GOPATH to thirdparty/go; doing a go get; adding in the BUILD rules needed for all of this.
3. Make it possible for grpc to generate service stubs from proto. This requires modifying bazel config (plugins=grpc, search for this in kythe for an example) and adding the implicit grpc dependencies. Kythe added this to their proto build rules with has_services flag. We're probably just going to want all of kythe's build rules for grpc.
4. Switch our code over to using grpc.

[ciera]

Part 1 is complete, D145.