Refactors SourcesViewController from Main.storyboard to new Sources.storyboard

Also refactors BannerCollectionViewCell to AppBannerCollectionViewCell to support initializing from code.

AltStore/Components/AppBannerCollectionViewCell.swift

@@ -0,0 +1,72 @@
+//
+//  AppBannerCollectionViewCell.swift
+//  AltStore
+//
+//  Created by Riley Testut on 3/23/20.
+//  Copyright © 2020 Riley Testut. All rights reserved.
+//
+
+import UIKit
+
+final class BannerCollectionViewCell: UICollectionViewCell
+{
+    let bannerView = AppBannerView(frame: .zero)
+    
+    private(set) var errorBadge: UIView!
+    
+    override init(frame: CGRect)
+    {
+        super.init(frame: frame)
+        
+        self.initialize()
+    }
+    
+    required init?(coder: NSCoder)
+    {
+        super.init(coder: coder)
+        
+        self.initialize()
+    }
+    
+    private func initialize()
+    {
+        self.contentView.autoresizingMask = [.flexibleWidth, .flexibleHeight]
+        self.contentView.preservesSuperviewLayoutMargins = true
+        
+        self.bannerView.translatesAutoresizingMaskIntoConstraints = false
+        self.contentView.addSubview(self.bannerView)
+        
+        let errorBadge = UIView()
+        errorBadge.translatesAutoresizingMaskIntoConstraints = false
+        errorBadge.isHidden = true
+        self.addSubview(errorBadge)
+        
+        // Solid background to make the X opaque white.
+        let backgroundView = UIView()
+        backgroundView.translatesAutoresizingMaskIntoConstraints = false
+        backgroundView.backgroundColor = .white
+        errorBadge.addSubview(backgroundView)
+                    
+        let badgeView = UIImageView(image: UIImage(systemName: "exclamationmark.circle.fill"))
+        badgeView.preferredSymbolConfiguration = UIImage.SymbolConfiguration(scale: .large)
+        badgeView.tintColor = .systemRed
+        errorBadge.addSubview(badgeView, pinningEdgesWith: .zero)
+        
+        NSLayoutConstraint.activate([
+            self.bannerView.topAnchor.constraint(equalTo: self.contentView.topAnchor),
+            self.bannerView.bottomAnchor.constraint(equalTo: self.contentView.bottomAnchor),
+            self.bannerView.leadingAnchor.constraint(equalTo: self.contentView.layoutMarginsGuide.leadingAnchor),
+            self.bannerView.trailingAnchor.constraint(equalTo: self.contentView.layoutMarginsGuide.trailingAnchor),
+            
+            errorBadge.centerXAnchor.constraint(equalTo: self.bannerView.trailingAnchor, constant: -5),
+            errorBadge.centerYAnchor.constraint(equalTo: self.bannerView.topAnchor, constant: 5),
+            
+            backgroundView.centerXAnchor.constraint(equalTo: badgeView.centerXAnchor),
+            backgroundView.centerYAnchor.constraint(equalTo: badgeView.centerYAnchor),
+            backgroundView.widthAnchor.constraint(equalTo: badgeView.widthAnchor, multiplier: 0.5),
+            backgroundView.heightAnchor.constraint(equalTo: badgeView.heightAnchor, multiplier: 0.5)
+        ])
+        
+        self.errorBadge = errorBadge
+    }
+}