Listen for incoming RFCOMM connections (act as BT slave).
Add a preference for disabling Bluetooth polling.

Fixed #122.
Avoid getting stuck with fast BT reconnections forever.
Kick off BT connection attempts when another BT device connects.

If you're getting into a car, your car is probably connecting to the
phone/audio socket on your phone - it's a good indicator that we should
re-scan (if you have polling enabled or BT devices). If you have a new
VI that can act as master and have polling disabled, this will have no
effect.

Fixed #121.