!clu #3416 Use plain protobuf and protoc

* Use the protobuf task to generate code for the cluster messages
* Convert the serializer to use plain protobuf instead of scalabuff
Merge pull request #1733 from akka/wip-3416-change-cluster-to-plain-protobuf-ban

!clu #3416 Use plain protobuf and protoc
Merge remote-tracking branch: upstream/master