Implement background service to force location update

[valkriaine]

Google location service manages geofencing, which means there may be a delay when the Android system detects that the user has entered a Mutified area. Mutify will still work, but it won't be as responsive.
By implementing a simple background service that repeatedly requests location updates (nothing more), we can force Google location service to respond to geofencing transitions more often, therefore making Mutify more responsive.