Handle exception when device has gone away on exit

There will be more of these to come, essentially if the device is pulled
out we can throw. It's not worth checking IsConnected everywhere since
you'll still need to try/catch for the case where it gets yanked and
IsConnected hasn't caught on yet.
Proper detection of Band connect / disconnect

* Timer to continually search for a Band / make sure the Band is still
there
* Progress Dialog that pops up on launch and when the Band is
disconnected