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/actor/mailbox/DurableMailboxDocTestBase.java

@@ -36,7 +36,7 @@ public class DurableMailboxDocTestBase {
   @Test
   public void configDefinedDispatcher() {
     //#dispatcher-config-use
-    ActorRef myActor = system.actorOf(new Props(MyUntypedActor.class).
+    ActorRef myActor = system.actorOf(Props.create(MyUntypedActor.class).
         withDispatcher("my-dispatcher"), "myactor");
     //#dispatcher-config-use
     myActor.tell("test", null);