Put in support for CALLBACK_TYPE_MATCH_LOST

[yaronyg]

In Marshmallow (api 23) a new bluetooth.le callback value CALLBACK_TYPE_MATCH_LOST was added to let the system explicitly communicate when it no longer is receiving advertisements from a device we have previously seen. We need to honor this callback and issue a peerAvailabilityChanged event when it occurs.

Note that it's unclear if implementing this feature is even worth the time. There are lots of reasons why we could lose connection with the BLE radio but still be able to reach the peer via Bluetooth (for example, we turn down BLE power when we are in the background but when we use Bluetooth we always have full power so we can reach farther with Bluetooth than BLE in some cases). We need to make sure this work is worth doing.