Revises Auth flow UI

AltStore/Authentication/InstructionsViewController.swift

@@ -0,0 +1,50 @@
+//
+//  InstructionsViewController.swift
+//  AltStore
+//
+//  Created by Riley Testut on 9/6/19.
+//  Copyright © 2019 Riley Testut. All rights reserved.
+//
+
+import UIKit
+
+class InstructionsViewController: UIViewController
+{
+    var completionHandler: (() -> Void)?
+    
+    var showsBottomButton: Bool = false
+    
+    @IBOutlet private var contentStackView: UIStackView!
+    @IBOutlet private var dismissButton: UIButton!
+    
+    override func viewDidLoad()
+    {
+        super.viewDidLoad()
+        
+        if UIScreen.main.isExtraCompactHeight
+        {
+            self.contentStackView.layoutMargins.top = 0
+            self.contentStackView.layoutMargins.bottom = self.contentStackView.layoutMargins.left
+        }
+        
+        self.dismissButton.clipsToBounds = true
+        self.dismissButton.layer.cornerRadius = 16
+        
+        if self.showsBottomButton
+        {
+            self.navigationItem.hidesBackButton = true
+        }
+        else
+        {
+            self.dismissButton.isHidden = true
+        }
+    }
+}
+
+private extension InstructionsViewController
+{
+    @IBAction func dismiss()
+    {
+        self.completionHandler?()
+    }
+}