Fix freeze when stopping tracking from watch

[skros89]

This fixes #12 .
Previously when stopping tracking from watch the app would freeze because the exit timer is not started.

[Artaud]

Many thanks for your pull request! This wouldn't probably be the issue, let me explain:
there are two methods, forceExit() and normalExit()

forceExit() does what you'd expect: if the phone is connected, send a "STOPPING" message, and start an exit timer right away.

however normalExit() just sends the "STOPPING" message, and shouldn't start the exit timer (unless the phone is disconnected), because when the phone addon gets the STOPPING message, it will acknowledge receiving it by sending a "StopApp" message back. This will then start the exit timer.
So starting the exit timer right in the normalExit() method would break this ack.

[skros89]

Oh yeah, I see. So this is more of a bad workaround, the issue is probably that the watch doesn't receive the "StopApp" message and stays stuck on stopping.