title: Force UICollectionView to stop scrolling
body: <p>A user performs a quick swipe gesture to make a UICollectionView start scrolling (it will gradually come to an halt).</p>
  
  <p>How can I programmatically force the scrolling to come to an immediate stop?
  To clarify, I want to allow the deceleration but I need to be able to stop it in code.</p>