make EventHandler non-global

- add Logging trait for nicer interface
- add EventHandlerLogging class for offering the nice interface from
  app.log
- add eventHandler instance to app and use that for all internal logging
  (this means that some places (dispatchers, remoting) were infiltrated
  by app just to do logging, but I think we'll need app in there soon
  enough for other reasons)

akka-tutorials/akka-tutorial-second/src/main/scala/Pi.scala

@@ -108,9 +108,9 @@ object Pi extends App {
     master.?(Calculate, Timeout(60000)).
       await.resultOrException match { //wait for the result, with a 60 seconds timeout
         case Some(pi) ⇒
-          EventHandler.info(this, "\n\tPi estimate: \t\t%s\n\tCalculation time: \t%s millis".format(pi, (now - start)))
+          app.eventHandler.info(this, "\n\tPi estimate: \t\t%s\n\tCalculation time: \t%s millis".format(pi, (now - start)))
         case None ⇒
-          EventHandler.error(this, "Pi calculation did not complete within the timeout.")
+          app.eventHandler.error(this, "Pi calculation did not complete within the timeout.")
       }
   }
 }