Deprecate actorFor in favor of ActorSelection, see #3074

* Deprecate all actorFor methods
* resolveActorRef in provider
* Identify auto receive message
* Support ActorPath in actorSelection
* Support remote actor selections
* Additional tests of actor selection
* Update tests (keep most actorFor tests)
* Update samples to use actorSelection
* Updates to documentation
* Migration guide, including motivation
Merge pull request #1277 from akka/wip-3074-deprecate-actorFor-patriknw

Deprecate actorFor in favor of ActorSelection, see #3074