Added the following for increased LLBadge functionality:
 * Panels now choose whether or not they accept buttons as children, which they
   do by default.
 * UI controls now shuffle controls with "requests_front" to the front of their
   children list at postBuild time.
 * Badges are set to "requests_front" by default
 * Badges now accept border image and color attributes

 Reviewed by Callum