+act #3770 Added Java 8 friendly APIs for Actor and FSM

* This is a WIP to get some feedback so some API doc is missing.
* There is both a maven and an sbt sample project in the same sample that needs to be built separately. You can choose whichever.
* Once sbt 0.13.1 is final it can be Activatorified!
* No automatic Java 8 tests until we find a workaround since sbt does not support compiling with a different version of javac than the one running sbt https://github.com/sbt/sbt/issues/887 
* To test the sample project you need to publish the artifacts locally from sbt using publishLocal or publishM2. Only akka-actor and akka-testkit are needed.