enhancement: option to pause server play on interruptions

[grobian]

When e.g. a phonecall comes in while playing music, the app is paused, however the server keeps playing. So after the phonecall finishes, and the app is resumed/played, the server never paused and thus you might end up in a couple of songs later in your playlist. (Apart from that local playback seems silent after this resume, possibly related, see issue #96.)

It would be nice if there were an option to treat these interruptions from control such that the server stops playing. This might not be desirable for every situation, but suppose I'd be playing on some home-audio and I'd receive a phonecall, it would make sense to stop the music (or reduce its volume) to aid making the phonecall.