title: Add Logout Button To be visible everywhere in an iPhone application
body: <p>I am building an iPhone application that requires the user to enter his credentials in order to use the application and can sign out in any moment. </p>
  
  <p>I have used <code>UITabBarController</code> to navigate through my views, now I need to add a Logout button in a way that it is available/visible all the time.</p>
  
  <p>Can anybody suggest a solution or best practice for this case?</p>