title: How to add HeaderView in UICollectionView like UITableView's tableHeaderView
body: <p>How can I add a header view / top view (not section header) at the top of a <code>UICollectionView</code>?</p>
  
  <p>It should act excactly as <code>UITableView</code>'s <code>tableHeaderView</code> property.</p>
  
  <p>So it needs to sit on top of the first section header view (before the section at index 0), scroll along with the rest of the content, and have user interaction.</p>
  
  <p>The best I've come up with so far is to make a special XIB (with <code>MyCollectionReusableView</code> subclass of <code>UICollectionReusableView</code> as the File's owner) for the first section header view that is big enough to also contain my subviews in header, it's kind of a hack, I think, and I haven't managed to detect touches.</p>
  
  <p>Not sure if I can make my <code>MyCollectionReusableView</code> subclass to allow touches or there's a better way.</p>