title: How to hide NSTableView gridlines / seperators for empty items
body: <p>I have a large NSTableView with only a few items, which are separated by gridlines / separators.  All is great apart from the fact that, below the items, are a bunch of gridlines, for empty items.  How is it possible to show gridlines for items that exist, but to just have plain background for non existent items?</p>
  
  <p>Note: UITableView has a way to set a footerView - this same method is not possible with NSTableView, otherwise it would just be a case of setting a big empty view as the footer...</p>