title: How to hide back button title on iOS7 with NavigationController
body: <p>I have a NavigationController based iOS7 app , on this I want to hide the back button text which is displayed along with the chevron. Is there a way out to  this ? I tried setting empty string to the back button title , tried empty title on previous view as well seems like if it finds empty title it replaces that with "Back" text.</p>
  
  <p>Please help</p>
  
  <p>Thanks</p>