Fix GPS settings change listener in LocManager

Bug 7051185

- Register a ContentObserver to track settings changes rather than
  opening up a Cursor with a ContentQueryMap.

- Move updateProvidersLocked into init to assure that the
  ContentObserver does not miss any changes.

- Move blacklist and fudger creation before loadProvidersLocked to
  improve code readability.

Change-Id: I4d3e19fa33401c384bc2b00658d4336ea119e0e5