[AltStoreCore] Refactors core AltStore logic into AltStoreCore framework

AltStoreCore will contain all shared AltStore code between AltStore and any app extensions. Initially, it includes all AltStore model logic.

AltStoreCore/Patreon/Tier.swift

@@ -0,0 +1,50 @@
+//
+//  Tier.swift
+//  AltStore
+//
+//  Created by Riley Testut on 8/21/19.
+//  Copyright © 2019 Riley Testut. All rights reserved.
+//
+
+import Foundation
+
+extension PatreonAPI
+{
+    struct TierResponse: Decodable
+    {
+        struct Attributes: Decodable
+        {
+            var title: String
+        }
+        
+        struct Relationships: Decodable
+        {
+            struct Benefits: Decodable
+            {
+                var data: [BenefitResponse]
+            }
+            
+            var benefits: Benefits
+        }
+        
+        var id: String
+        var attributes: Attributes
+        
+        var relationships: Relationships
+    }
+}
+
+public struct Tier
+{
+    public var name: String
+    public var identifier: String
+    
+    public var benefits: [Benefit] = []
+    
+    init(response: PatreonAPI.TierResponse)
+    {
+        self.name = response.attributes.title
+        self.identifier = response.id
+        self.benefits = response.relationships.benefits.data.map(Benefit.init(response:))
+    }
+}