title: Relayout UICollectionView when tap the header
body: <p>I'm trying to do collapsible <code>UICollectionView</code>. The collection view should show smaller items in section when user tap on the header.</p>
  <p><a href="https://i.stack.imgur.com/a2pJZ.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/a2pJZ.png" alt="" /></a></p>
  
  <p>Please suggest me where should I start. Should I go for custom <code>UICollectionViewLayout</code> or <code>UICollectionViewFlowLayout</code></p>
  <p>(I think the second one is more interesting)? If there are other ways of doing this stuff, please give me some resources so I do further research.</p>