Handle MIDI disconnections

[ApolloFops]

Handle MIDI device disconnections, and attempt to reconnect. The MIDI connection state should probably be reported to the server somehow, and there should be an option to reset values to their defaults when this happens (trigger the same thing as #6, but just on device disconnection instead of on client disconnection).

[ApolloFops]

I've been experimenting with this a bit, and Java's default MIDI backend doesn't actually check for devices after the JVM initially starts, so there's no way to even tell the device has disconnected, let alone reconnect to it (there's also a ton more limitations, see the CoreMidi4J README for more info). I may implement something where there is some sort of heartbeat (MIDI active sense?) which, if not detected, triggers a full restart of the bridge program, but I think it will be better to just switch to a different MIDI backend altogether, since Java's one is pretty limited (it also has problems with SYSEX messages and other various things).

[ApolloFops]

After looking into this a bit more, it actually looks like it should be possible to do. The issues I was talking about in the previous comment only affect OSX, and CoreMidi4J fixes those problems (and also the SysEx things), making it possible (and actually pretty easy) to monitor for MIDI device changes.