title: Snap to center of a cell when scrolling UICollectionView horizontally
body: <p>I know some people have asked this question before but they were all about <code>UITableViews</code> or <code>UIScrollViews</code> and I couldn't get the accepted solution to work for me. What I would like is the snapping effect when scrolling through my <code>UICollectionView</code> horizontally - much like what happens in the iOS AppStore. iOS 9+ is my target build so please look at the UIKit changes before answering this.</p>
  
  <p>Thanks.</p>