title: Navigation title not showing on the center after pushing view controller onto NavigationController
body: <p>I have a <code>UINavigationController</code> with the root controller as a <code>UICollectionViewController</code> called <code>HomeController</code> which I have set up in my AppDelegate:</p>
  
  <pre><code>import UIKit
  
  @UIApplicationMain
  class AppDelegate: UIResponder, UIApplicationDelegate {
  
      var window: UIWindow?
  
      func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -&gt; Bool {
  
          window = UIWindow(frame: UIScreen.main.bounds)
          window?.makeKeyAndVisible()
  
          let layout = UICollectionViewFlowLayout()
          window?.rootViewController = UINavigationController(rootViewController: HomeController(collectionViewLayout: layout))    
          return true
      }
      ...
  }
  </code></pre>
  
  <p>Now in my HomeController I am trying to set the center text of a new <code>ViewController</code> (<code>dummySettingViewController</code>) I push onto the NavigationController as shown below:</p>
  
  <pre><code>class HomeController: UICollectionViewController, UICollectionViewDelegateFlowLayout {
      ...
      func showControllerForSettings(setting: SettingModel) {
          let dummySettingViewController = UIViewController()
          dummySettingViewController.view.backgroundColor = UIColor.white
          navigationController?.pushViewController(dummySettingViewController, animated: true)
          //THIS DOESN'T SET THE dummySettingViewController TITLE TEXT
          self.navigationItem.title = "TEST_TITLE"
          navigationController?.navigationBar.tintColor = UIColor.white
          navigationController?.navigationBar.titleTextAttributes = [NSForegroundColorAttributeName: UIColor.white]
  
      }
      ...
  }
  </code></pre>
  
  <p>My problem is in this line <code>self.navigationItem.title = "TEST_TITLE"</code>. It doesn't set the center title text of the new <code>dummySettingViewController</code> that is pushed onto the <code>navigationController</code> but instead sets the <code>back button</code> text in the <code>NavBar</code> of the <code>dummySettingViewController</code> to <code>TEST_TITLE</code>.</p>
  
  <p>In this line: <code>self.navigationItem.title = "TEST_TITLE"</code> when I use <code>self</code> is that referring to the <code>HomeViewController</code> navigationItem or the <code>NavBar</code> of the <code>navigationController</code>? I am confused on how the <code>NavBar</code> on each <code>ViewController</code> works? Can someone please clarify this?</p>