[AltStore] Revises database model to support both store apps and sideloaded apps

AltStore/Protocols/AppProtocol.swift

@@ -0,0 +1,38 @@
+//
+//  AppProtocol.swift
+//  AltStore
+//
+//  Created by Riley Testut on 7/26/19.
+//  Copyright © 2019 Riley Testut. All rights reserved.
+//
+
+import Foundation
+import AltSign
+
+protocol AppProtocol
+{
+    var name: String { get }
+    var bundleIdentifier: String { get }
+    var url: URL { get }
+}
+
+extension ALTApplication: AppProtocol
+{
+    var url: URL {
+        return self.fileURL
+    }
+}
+
+extension App: AppProtocol
+{
+    var url: URL {
+        return self.downloadURL
+    }
+}
+
+extension InstalledApp: AppProtocol
+{
+    var url: URL {
+        return self.fileURL
+    }
+}