[AltStore] Adds basic Patreon integration

- Lists beta versions of apps when signed in to Patreon
- Lists names of Patrons with the Credits benefit

AltStore/Patreon/Campaign.swift

@@ -0,0 +1,27 @@
+//
+//  Campaign.swift
+//  AltStore
+//
+//  Created by Riley Testut on 8/21/19.
+//  Copyright © 2019 Riley Testut. All rights reserved.
+//
+
+import Foundation
+
+extension PatreonAPI
+{
+    struct CampaignResponse: Decodable
+    {
+        var id: String
+    }
+}
+
+struct Campaign
+{
+    var identifier: String
+        
+    init(response: PatreonAPI.CampaignResponse)
+    {
+        self.identifier = response.id
+    }
+}