title: how to Unregister ContentObserver on AppWidgetProvider's-OnDisabled()
body: <p>in my appWidget I register some ContentObservers' in the OnEnabled() method.</p>
  
  <p>so I've been told that I should unregister my ContentObserver's in the OnDisabled() method of my widget.</p>
  
  <p>as far as I know, the only way to do so is by context.getContentResolver().unregisterContentObserver(observer);</p>
  
  <p>the problem is: How do I save a pointer to the ContentObserver that I've registered in the OnEnabled() method, in order to delete it?</p>