title: Changing Done UIBarButtonItem's background image
body: <p>I want to make a custom UIBarButtonItem to represent the Done button.
  I want to able to internationalize the app, so I want the text to be directly editable. To take into account different lengths of the "Done" Label, I've designed an stretchableImage. Is it possible to directly change the default edit button background or is a custom UIBarButtonItem needed? If so, what would be the way to dynamically resize the background stretchableImage according to the length of the label?</p>