* add java support in akka-actor module in the class Abstract.ActorContext by adding the setReceiveTimeout and CancelReceiveTimeout
* add akka.actor.AbstractActor#ActorContext cancelReceiveTimeout and setReceiveTimeout to mima-excludes file
* removed scala.concurrent.duration dependency in ActorDocTest and add new method expectTerminated with java.time.Duration support in TestKit
* used java.time.Duration as default import
* Identical contents in scala/cluster-metrics.md and java/cluster-metrics.md for easier review
* Replace java/cluster-metrics.md with a symlink to scala/cluster-metrics.md
* Fix typo