=con #3616 Fix failing ClusterClientSpec

* client connected to fourth node, but the replication check didn't
  include that node
=rem #3606 Properly reset system message buffer between remote sys restarts
!per #3618 Cleanup duplication of life cycle hooks in Processor

 - introduce around life cycle hooks for symmetry with aroundReceive
 - no custom processor-specific life cycle hooks needed any more
 - preStart and preRestart can be overridden with empty implementation
    (interceptors ensure that super.preXxx calls are still executed)
 - all around life cycle hooks can be final
 - standard life cycle hooks are non-final to preserve composability with existing traits (FSM, ...)
Merge pull request #1739 from akka/wip-3616-ClusterClientSpec-patriknw

=con #3616 Fix failing ClusterClientSpec
!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 pull request #1737 from drewhk/wip-3606-resend-unfulfillable-drewhk

=rem #3606 Properly reset system message buffer between remote sys restarts
Merge pull request #1742 from eligosource/wip-3618-cleanup-lifecycle-hooks-krasserm

!per #3618 Cleanup duplication of life cycle hooks in Processor