title: Top most ViewController under UIAlertController
body: <p>I am using the following extension to find the <a href="https://stackoverflow.com/a/30572389/1341180">top most ViewController</a>. 
  If alert is presented, the code above gives <code>UIAlertController</code>.
  How do I get top view controller <strong>under</strong> <code>UIAlertController</code>? </p>