implementato il layout della schermata operazione
modifiche all'interfaccia grafica

perché ho tolto il menù?
https://groups.google.com/forum/#!topic/android-developers/G_D3pKnGLt0

"The user doesn't, the system handles this automatically. That's what
 the activity lifecycle (especially onPause/onStop/onDestroy) is for.
 No matter what you do, do not put a "quit" or "exit" application
 button. It is useless with Android's application model. This is also
 contrary to how core applications work.

 Note that when the user presses Back, the Activity is destroyed."

 Quindi non conviene mettere un menù in Android perché non serve. Gestisce già tutto lui