Add immersive mode for photo viewer
Remove junk file
Bug fixes around photo viewer state management

* Can now call super.onSavedInstanceState from PhotoViewerActivity
  without IllegalStateException, this can only improve state management.

* Comments / photo info dialog now keep their state on config change.

* PhotoInfoFragment no longer removes menu items.

* Simplified toggling of the dialogs, no more mCommentsFragmentShowing
  maintenance.

Way too much refactoring which unfortunately makes the diff almost
impossible to read.