title: NSCollectionViewItems shaking and with X to remove
body: <p>On Launchpad we have basically a big collection view with app icons. When you hold an app (press down with the cursor and don't stop) for a very long time, all the icons start to shake, and a little 'x' appears in the top left hand corner of each one of them, which makes removing items very easy.</p>
  
  <p>I would like to know if there is some method already implemented in the API which allow us to reproduce that same behavior in a regular NSCollectionView.</p>
  
  <p>I've checked <code>NSCollectionView</code> and <code>NSCollectionViewDelegate</code> documentations in Apple's Mac Developer Library, however I haven't seeing anything related to that. Should that be done <em>manually</em>? If so, how can I make the collection view items shake?</p>