IMPORTANT! CORRECTED CRITICAL BUG. At GoogleMapFragment, on the method
onStop(), the location clinet should never set to null.
Implementing sharedpreferences for the state of the google map buttons.
Selectable state implemented.
SharedPreferences for the Map State completed. Now, the map state is
saved every time the map fragment is destroyed and restore its state
whenever the map fragment is being instantiated again. OBS! When the
application is being destroyed the editor of the sharedpreferences is
cleared out.