remove app argument from Dispatchers

(cascading into all dispatchers, mailboxes, other stuff; had to move
deadLetter stuff to ActorSystem again and split its initialization due
to cyclic dependency)

akka-actor-tests/src/test/scala/akka/testkit/CallingThreadDispatcherModelSpec.scala

@@ -11,7 +11,7 @@ import org.junit.{ After, Test }
 class CallingThreadDispatcherModelSpec extends ActorModelSpec {
   import ActorModelSpec._
 
-  def newInterceptedDispatcher = new CallingThreadDispatcher(app, "test") with MessageDispatcherInterceptor
+  def newInterceptedDispatcher = new CallingThreadDispatcher(app.deadLetterMailbox, app.eventStream, app.scheduler, "test") with MessageDispatcherInterceptor
   def dispatcherType = "Calling Thread Dispatcher"
 
 }