title: UICollectionView sticky header in swift
body: <p>I'm trying to create a sticky supplementary header, which stays on top all the time and won't response to scrolling events. The solutions I found so far still react on bounch scrolling and are fixed using a custom flowLayout, which will probably be the fix for mine issue as well.</p>
  
  <p>The reason I want it this way is that the header is used on other places and should be reusable. I'm hoping this could be solved this way and I don't have to create a separated view.</p>
  
  <p>As I'm doing this in Swift, it would be great to have an example in Swift.</p>