title: Add shadow to a UITabbar in iOS8
body: <p>I wanna add a simple shadow to my UITabbar. 
  I added a shadow image (a 10x1 gradient) to my project / related storyboard property.</p>
  
  <p>The image should be repeated by itself, shouldn't it?</p>
  
  <p>Nevertheless, there is no shadow in the design mode as well no shadow if I launch the application. </p>
  
  <p>Would could be wrong?</p>