title: Add selection animation to a UIButton
body: <p>I have a UIButton in one of my ViewControllers with three different state images (normal, highlighted and selected). When I press this button, it becomes highlighted and when I release it, selected. I want to make an animation that changes the highlighted image of the button to the selected one in 4 seconds with a fadeIn or so. </p>
  
  <p>Any suggestion?</p>