title: Perform "use photo" button on custom image picker overlay
body: <p>I am creating fully custom overlay for image picker controller. First stage is easy: I am get first view with record/take a shot button, which call <code>takePicture()</code> method.</p>
  
  <p>Next stage is change UI to "Retake" or "Use photo" which is also with my own design. "Retake" probably can be imitated by calling <code>presentViewController</code> again. How should I imitate "Use photo" button? </p>