Druzic
 - Add Backkey event.
 - if you pressing backkey in melody or accompaniment scene, ask your
   save file.
Druzic
 - Just working
Druzic
 - need to fix random listview sorting bug.
 - not playback melody
 - failed save melody
Druzic
 - Complete Thread-safety.
 - bugfix (after double touch, speak sound at the same time