title: UINavigationBar custom back button without title
body: <p>How can I customize the navigation back button in iOS 7 and above without title? (i.e. with the arrow only)</p>
  
  <pre><code>self.navigationItem.leftBarButtonItem = self.editButtonItem;
  </code></pre>
  
  <p>I'm just wondering if they have any self.backButtonItem;</p>
  
  <p>OR </p>
  
  <p>something like this?</p>
  
  <pre><code>self.navigationItem.leftBarButtonItem = [[UIBarButtonItem alloc]
                     initWithBarButtonSystemItem:UIBarButtonSystemItemBACK 
                     target:self action:@selector(back)];
  </code></pre>