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/camel/HttpExample.scala

@@ -43,8 +43,8 @@ object HttpExample {
     // to your boot class.
     val system = ActorSystem("some-system")
     val httpTransformer = system.actorOf(Props[HttpTransformer])
-    val httpProducer = system.actorOf(Props(new HttpProducer(httpTransformer)))
-    val httpConsumer = system.actorOf(Props(new HttpConsumer(httpProducer)))
+    val httpProducer = system.actorOf(Props(classOf[HttpProducer], httpTransformer))
+    val httpConsumer = system.actorOf(Props(classOf[HttpConsumer], httpProducer))
     //#HttpExample
 
   }