 AttributeError: 'Play' object has no attribute 'nextTrack'

```
   File "/home/equant/jukebox/main.py", line 549, in check_for_rotary_dial_input
     self.sm.current_screen.handle_input(readlineString)
   File "/home/equant/jukebox/main.py", line 480, in handle_input
     app.musicPlay.nextTrack()
 AttributeError: 'Play' object has no attribute 'nextTrack'

```