Geofencing for MozStumbler.

Updates as requested by @cpeterso.

Even better geofencing - menu option and status display.

Introduction of one way communication from the main thread to the BlockList.

Experimental geofencing indicator.

Changes as requested by @cpeterso.

Bug fixes. Final touches.
Tiny fixup.

There was this remote chance that user could ask to geofence here, then turn the blocking off and on again causing trouble in the main activity code. This prevents such situation from occurring.