* because it will result in quarantine if failure detection triggers and that kind of coupling is exactly what is not desired for a ClusterClient * replace by simple heartbeat failure detection, DeadlineFailureDetector * DeadLetterSuppression
* rename ClusterReceptionistExtension to ClusterClientReceptionist
* rename DistributedPubSubExtension to DistributedPubSub
* new module akka-cluster-tools containing cluster singleton, distributed pub-sub, and cluster client