title: Get instance of main window controller in app delegate
body: <p>I know that, for iOS, you can reference the root view controller from the app delegate like so:</p>
  
  <p>var rootViewController = self.window!.rootViewController</p>
  
  <p>How does one reference the main window controller from the app delegate when targeting OS X? I would like to pass a variable (the managed object context) this way, as I have read that it is a good solution for referencing the moc.</p>