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

![device-2014-04-19-184039](https://cloud.githubusercontent.com/assets/2092627/2749646/9564a6d4-c814-11e3-8a84-9878ebcb636f.png)