clean up application structure

- introduce common parent for guardian and systemGuardian
- install deathWatch chain to ensure proper shutdown upon guardian’s
  death
- re-install stdout logger before detaching default loggers
- await app termination after running AkkaSpec tests (max 5sec, with
  warning logged if not stopped)

akka-actor/src/main/scala/akka/dispatch/Dispatcher.scala

@@ -107,7 +107,7 @@ class Dispatcher(
   protected[akka] def shutdown {
     val old = executorService.getAndSet(new LazyExecutorServiceWrapper(executorServiceFactory.createExecutorService))
     if (old ne null)
-      old.shutdown()
+      old.shutdownNow()
   }
 
   /**