title: UITableViewController - image background
body: <p>i have UITableViewController, and I'm trying to set a image background.
  the issue is the background image does not fit the whole screen, in other words, the image background <strong>does not</strong> stretch with the table cells.
  this my code</p>
  
  <pre><code>    let imgView =  UIImageView(frame: self.tableView.frame)
      let img = UIImage(named: "b2")
      imgView.image = img
      imgView.frame = CGRectMake(0, 0, self.tableView.frame.width, self.tableView.frame.height)
      imgView.contentMode = UIViewContentMode.ScaleAspectFill
      self.tableView.addSubview(imgView)
      self.tableView.sendSubviewToBack(imgView)
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/XxUrk.png" rel="noreferrer"><img src="https://i.stack.imgur.com/XxUrk.png" alt="enter image description here"></a></p>