title: Swift 3: How to set up UINavigationBar setBackgroundImage in AppDelegate
body: <p>I recently migrated from Swift 2 to Swift 3 and I'm stuck on one part.  In my AppDelegate, I'd set up the default settings for the UINavigationBar as coded below.  The challenge I'm having is that the setBackgroundImage is no longer recognized in Swift 3 and I can't find an alternative.  </p>
  
  <p>Has anyone had the same issue happen and been able to resolve it?</p>
  
  <pre><code>    let turquoiseBackgroundImage:UIImage = UIImage(named: "navigationBarTurqoise")!
  
  
      **// TODO Below is not working with Swift 3
      UINavigationBar.appearance().setBackgroundImage(turquoiseBackgroundImage, forBarPosition: .Default)**
  
  
      // Set up Back button to be white in Navigation bar
      UINavigationBar.appearance().barStyle = UIBarStyle.default
      UINavigationBar.appearance().tintColor = UIColor.white
  
      // Font Name and Size of Title in Navigation Bar
      if let font = UIFont(name: "TitilliumWeb-Light", size: 20) {
          UINavigationBar.appearance().titleTextAttributes = [NSFontAttributeName : font, NSForegroundColorAttributeName : UIColor.white]
      }
  
      // Remove hairline between navigation bar and anything below such as search bar
      UINavigationBar.appearance().shadowImage = UIImage()
  
      // Set up status bar (battery, time, etc.) to white
      UIApplication.shared.statusBarStyle = .lightContent
  </code></pre>