Added 'repeat' property to emulate 'setIndeterminate:' 

This adds the 'repeat' property to emulate the behaviour of the standard NSProgressIndicator. I.e. once the animation reaches the end, it will go back to the start again. The animation animates between the range that was used for the last setProgress:animated: call. It will also stop once the view has no subview anymore (to allow ARC to pick it up if it's not being used anymore).