title: UICollectionView reloadSections with animation
body: <p>I'd like to reload UICollectionView with some interesting animation. In UITableView there's a method called <code>reloadSections:withRowAnimation</code>.
  But in UICollectionView there's just <code>reloadSections</code>.</p>
  
  <p>How can I customize reloadSections animation? I definitely saw this in apps on the App Store.</p>