title: Nstableview group style for nsoutlineview
body: <p>I like the look of the group rows in the nstableview. In apple mail, the group sections like mailboxes and rss with that style too. </p>
  
  <p>Is there an easy way to make a group row or root item in an nsoutlineview to look like that? I think I have to override the willDisplayCell method...</p>