[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/Components/Keychain.swift

@@ -0,0 +1,88 @@
+//
+//  Keychain.swift
+//  AltStore
+//
+//  Created by Riley Testut on 6/4/19.
+//  Copyright © 2019 Riley Testut. All rights reserved.
+//
+
+import Foundation
+import KeychainAccess
+
+import AltSign
+
+@propertyWrapper
+public struct KeychainItem<Value>
+{
+    public let key: String
+    
+    public var wrappedValue: Value? {
+        get {
+            switch Value.self
+            {
+            case is Data.Type: return try? Keychain.shared.keychain.getData(self.key) as? Value
+            case is String.Type: return try? Keychain.shared.keychain.getString(self.key) as? Value
+            default: return nil
+            }
+        }
+        set {
+            switch Value.self
+            {
+            case is Data.Type: Keychain.shared.keychain[data: self.key] = newValue as? Data
+            case is String.Type: Keychain.shared.keychain[self.key] = newValue as? String
+            default: break
+            }
+        }
+    }
+    
+    public init(key: String)
+    {
+        self.key = key
+    }
+}
+
+public class Keychain
+{
+    public static let shared = Keychain()
+    
+    fileprivate let keychain = KeychainAccess.Keychain(service: "com.rileytestut.AltStore").accessibility(.afterFirstUnlock).synchronizable(true)
+    
+    @KeychainItem(key: "appleIDEmailAddress")
+    public var appleIDEmailAddress: String?
+    
+    @KeychainItem(key: "appleIDPassword")
+    public var appleIDPassword: String?
+    
+    @KeychainItem(key: "signingCertificatePrivateKey")
+    public var signingCertificatePrivateKey: Data?
+    
+    @KeychainItem(key: "signingCertificateSerialNumber")
+    public var signingCertificateSerialNumber: String?
+    
+    @KeychainItem(key: "signingCertificate")
+    public var signingCertificate: Data?
+    
+    @KeychainItem(key: "signingCertificatePassword")
+    public var signingCertificatePassword: String?
+    
+    @KeychainItem(key: "patreonAccessToken")
+    public var patreonAccessToken: String?
+    
+    @KeychainItem(key: "patreonRefreshToken")
+    public var patreonRefreshToken: String?
+    
+    @KeychainItem(key: "patreonCreatorAccessToken")
+    public var patreonCreatorAccessToken: String?
+    
+    private init()
+    {
+    }
+    
+    public func reset()
+    {
+        self.appleIDEmailAddress = nil
+        self.appleIDPassword = nil
+        self.signingCertificatePrivateKey = nil
+        self.signingCertificateSerialNumber = nil
+    }
+}