Fix selected change receiver being disabled

Previously, after changing the theme, trying to select a change no longer worked.
 This was because onPause was called after the last call to onResume.
 Registering/unregistering the listeners when the activity is started/stopped instead
 fixes this.
Fix bad merge in GsonRequest.

Change-Id: I964019cbfbbcdc421f9b578fefb8db230307c268