deprecate closure-taking Props factories, see #3081

- base Props on Deploy, Class and Seq[Any] (i.e. constructor args)
- remove deprecated Props usage from akka-docs sample code
- rewrite UntypedActorDocTestBase
- rewrite Java/Scala doc section on actor creation
- add migration guide entry

akka-docs/rst/java/code/docs/pattern/SupervisedAskSpec.java

@@ -18,7 +18,7 @@ public class SupervisedAskSpec {
       ActorRef supervisorCreator = SupervisedAsk
           .createSupervisorCreator(actorSystem);
       Future<Object> finished = SupervisedAsk.askOf(supervisorCreator,
-          Props.apply(someActor), message, timeout);
+          Props.create(someActor), message, timeout);
       return Await.result(finished, timeout.duration());
     } catch (Exception e) {
       // exception propagated by supervision