Deprecate actorFor in favor of ActorSelection, see #3074

Still some more things to do, but the review can start...

* [x] Deprecate all actorFor methods
* [x] resolveActorRef in provider
* [x] Identify auto receive message
* [x] Support ActorPath in actorSelection
* [x] Support remote actor selections
* [x] Additional tests of actor selection
* [x] Update tests (keep most actorFor tests)
* [x] Update samples to use actorSelection
* [x] Update cluster samples
* [x] Update rst documentation
* [x] Migration guide