Mopidy takes a long time to shut down when using Mopidy-AlarmClock

[rgov]

When Mopidy-AlarmClock is loaded (granted, with my changes, but I think this is unrelated to them), service mopidy restart seems to take a loooong time. There are no logs pointing the finger at anything, but my suspicion is that the timer thread (or threads, if they're constantly being created) are not getting the signal to shut down.

I looked around and Mopidy-GMusic also has a repeating timer, and its Pykka-aware backend seems to get an on_stop message that tells it to kill its timer. But I don't know how we can do the same thing without significantly changing.