Median RSSI, proximity zones, beacon object integration, and menu options.

* Using median instead of mean-shifting is giving better results for averaging while updating
* Beacons change color and the positioning method changes when within 0.8 m of a beacon
* `BeaconManager` and `MapActivity` now share usage of the same beacon objects
* Added menu options to toggle drawing beacon circles, and for restarting the Bluetooth adapter