key error if no retake button is configured

[derpeter]

If the gui is configured to not have a retake button the key retake is missing in mix.py

Traceback (most recent call last):
File "/home/pi/voctomix/voctogui/lib/connection.py", line 133, in on_loop
handler(*args)
File "/home/pi/voctomix/voctogui/lib/toolbar/mix.py", line 61, in on_best
self.mix['retake']['button'].set_sensitive(command != self.preview_controller.output)
KeyError: 'retake'
Traceback (most recent call last):
File "/home/pi/voctomix/voctogui/lib/toolbar/mix.py", line 57, in on_btn_clicked
self.mix['retake']['button'].set_sensitive(self.preview_controller.command() != self.preview_controller.output)
KeyError: 'retake'
Traceback (most recent call last):
File "/home/pi/voctomix/voctogui/lib/connection.py", line 133, in on_loop
handler(*args)
File "/home/pi/voctomix/voctogui/lib/toolbar/mix.py", line 61, in on_best
self.mix['retake']['button'].set_sensitive(command != self.preview_controller.output)
KeyError: 'retake'

this is triggert on every cut action