title: updateViewConstraints and orientation handling
body: <p>I've some questions about the  <code>updateViewConstraints</code> method:</p>
  
  <ol>
  <li>Why is <code>updateViewConstraints</code> called twice at the loading of the view controller? And why is it called when the view controlle is dismissed?</li>
  <li>In iOS 7.1 <code>updateViewConstraints</code> is not called when the orientation changes. In iOS 8 it is. Now I'm calling <code>updateViewConstraints</code> in <code>willRotateToInterfaceOrientation:duration</code>, which is up to iOS 7 only.</li>
  <li>Where should one add/remove subviews/child view controllers? Currently I'm doing this in <code>updateViewConstraints</code> because <code>UIDeviceOrientationDidChangeNotification</code> is called after <code>updateViewConstraints</code>. The views have to be available before the new constraints are added.</li>
  </ol>