Use simplified callbacks

The reference app is now updated to use the simplified callbacks from the region-and-beacon-name-access branch of proximitykit-android.  

The ProximityKitBeacon, ProximityKitBeaconRegion and ProximityKitGeofenceRegion classes now provide easy access to the PK name field and all PK attributes.  And these objects are now returned by the ranging and monitoring callbacks.

Should have done this six months ago!