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/actor/Scheduler.scala

@@ -130,7 +130,7 @@ class DefaultScheduler extends Scheduler {
     }
   }
 
-  private[akka] def shutdown() { service.shutdown() }
+  private[akka] def shutdown() { service.shutdownNow() }
 }
 
 private object SchedulerThreadFactory extends ThreadFactory {