title: Find ViewController in NavigationController with special key
body: <p>I have a NavigationController with different ViewControllers. Sometimes I want to push a ViewController to NavigationController, which is already included.
  In this case I want to move to the existing from TopController, and pop all other ViewControllers between top and the existing one.</p>
  
  <p>Is there a way to give a ViewController a special id (for example a NSString), to find him later in "NavigationController.viewControllers"?
  Or should I use a seperate Dictionary to manage my ViewControllers?</p>
  
  <p>Or is there a better way, I dont consider.</p>
  
  <p>best regards</p>