SysUI: Only create controllers if they are null.

The various controllers, such as mLocationController, get recreated
every time the status bar is recreated due to a theme change.  We
should only need to create these if they are null, otherwise use
the controller as is.  Also, each of these controlers registers
themselves as a broadcast receiver and are never unregistered before
recreating them.

Change-Id: I6215aae5a82b7ced8f0f25cf592a804d38825260