title: Cannot set Title Text Attributes of UIBarButtonItem for Highlighted state
body: <p>During customization stage I was trying to set the title attributes of <code>UIBarButtonItem</code> instances used in the app for both states: <code>UIControlStateNormal</code> and <code>UIControlStateHighlighted</code>. </p>
  
  <p>For the <code>.Normal</code> button's state the following code works fine:</p>
  
  <pre><code>barButton.setTitleTextAttributes([NSForegroundColorAttributeName: UIColor.greenColor(), NSFontAttributeName: UIFont.systemFontOfSize(18.0)], forState: .Normal)
  </code></pre>
  
  <p>However, if I change the state parameter to <code>.Highlighted</code> the code has no effect. Firstly I thought maybe it's something wrong with the current app so I created a new project from scratch with just one toolbar and one <code>UIBarButtonItem</code> but the issue is still here.</p>
  
  <p>Even setting the title attributes for all items by using the appearance proxy has no effect so the next code does nothing:</p>
  
  <pre><code>// Has no effect
  UIBarButtonItem.appearance().setTitleTextAttributes([NSForegroundColorAttributeName: UIColor.redColor(), NSFontAttributeName: UIFont.systemFontOfSize(28.0)], forState: .Highlighted)
  
  // This one has no effect too  
  UIBarItem.appearance().setTitleTextAttributes([NSForegroundColorAttributeName: UIColor.greenColor(), NSFontAttributeName: UIFont.systemFontOfSize(28.0)], forState: .Highlighted)
  </code></pre>
  
  <p>Am I missing something or is it Apple's bug? The documentation doesn't mention any cautions regarding <code>UIBarButtonItem</code> title attributes for highlighted states.</p>