title: Place activity indicator over uitable view
body: <p>I've placed an Activity indicator in a <code>UITableView</code> within the storyboard.
  How can I center it in the middle of the screen and in front of the table view?</p>
  
  <p>I've tried:</p>
  
  <pre><code>self.activityIndicator.center = self.tableView.center
  </code></pre>
  
  <p>But now, the activity indicator is in the top-middle of the view!</p>