[enhancement] Play a notification if mapping is stopped

[bluepup]

I sometimes map and for some reason an error occurs and the mapping is stopped. I can start the mapping by pressing the start button, but because ttnmapper does not give a audible warning I'm unaware until a lot of time is wasted or I'm at the end of the trip.

Play a warning tone that indicates that the recording has stopped to prevent this. The tone should not only play when an error occurs but every time the recording is stopped or started (by hand or error).

That would be a great thing!

[jpmeijers]

After some other bug fixes I am not sure if this is still a necessary feature

[bluepup]

Stability has improved a lot indeed. So this is only nice to have now.
Maybe playing a sound when starting and stopping is still a good idea if it is not too much trouble to implement.