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/scala/code/docs/actor/FaultHandlingDocSample.scala

@@ -168,7 +168,7 @@ class CounterService extends Actor {
 
     case Entry(k, v) if k == key && counter == None ⇒
       // Reply from Storage of the initial value, now we can create the Counter
-      val c = context.actorOf(Props(new Counter(key, v)))
+      val c = context.actorOf(Props(classOf[Counter], key, v))
       counter = Some(c)
       // Tell the counter to use current storage
       c ! UseStorage(storage)