title: Find height of the empty space in a UITableView
body: <p>In my UITableView I need to position an UIView at the footer of the table and outside of the screen. For example, the "Push to refresh" functionality (like Twitter app) is at the begging of the table and outside the screen, I need the same but at the bottom.</p>
  
  <p>If I have enough rows with a total height bigger than the screen height I don't have any problem, but if I haven't any rows I can't position muy view.</p>
  
  <p>So I need to add a blank cell (custom cell) to my table to fill the empty space between the last cell and the bottom of the screen, how can I do it? How can I Know the height of the empty space?</p>
  
  <p>Thank you very much form your help.</p>