UI/UX: add navigation button

Add back button to initial walkthrough

Change-Id: I25e2dd03d8ae862fb2a23d61c6e6289ecc01e4e7
Reviewed-by: Andreas Traczyk <andreas.traczyk@savoirfairelinux.com>

Ring/Ring/Features/Walkthrough/Welcome/WelcomeViewController.swift

@@ -58,7 +58,9 @@ class WelcomeViewController: UIViewController, StoryboardBased, ViewModelBased {
 
     override func viewWillAppear(_ animated: Bool) {
         super.viewWillAppear(animated)
-        self.navigationController?.setNavigationBarHidden(true, animated: false)
+        self.navigationController?.navigationBar.setBackgroundImage(UIImage(), for: UIBarMetrics.default)
+        self.navigationController?.navigationBar.shadowImage = UIImage()
+        self.navigationController?.navigationBar.isTranslucent = true
     }
 
 }