Add @SerialVersionUID to Serializable classes. See #1786

* @SerialVersionUID(1L)
* UntypedActorFactory serialization, and test
* Removed Serializable from Serializers

akka-actor/src/main/scala/akka/actor/Props.scala

@@ -103,6 +103,7 @@ object Props {
  *  Props props = new Props(MyActor.class).withRouter(new RoundRobinRouter(..));
  * }}}
  */
+@SerialVersionUID(1L)
 case class Props(
   creator: () ⇒ Actor = Props.defaultCreator,
   dispatcher: String = Dispatchers.DefaultDispatcherId,