title: add additional buttons in UITableView swipe
body: <p>Currently I am using NSFetchedResultsController to handle tableviews.
  I am wondering is there any way to add additional buttons like the delete button in swipe operation? </p>
  
  <p>I am thinking about to subclass it. But find nothing relevant in help docs to my problems.</p>
  
  <p>Thanks in advance.</p>