gRPC definitions for u-bmc

When updating the .proto file, make sure to update and commit the updated Go implementation. The reason for this is to make it trivial to include the protocol definitions without having to do a pre-build step in Go.

1. Make sure you have protoc installed. On Debian this can be installed via apt-get install protobuf-compiler.

2. Install protoc-gen-go by running go get -u github.com/golang/protobuf/protoc-gen-go.

3. Run task proto:protogen to update the .pb.go file(s).