[AltServer] Moves core ConnectionManager logic to AltKit

Refactors ConnectionManager to use arbitrary RequestHandlers and ConnectionHandlers. This allows the core AltServer request logic to be shared across different targets with different connection types.

AltKit/Connections/ALTConnection.h

@@ -0,0 +1,23 @@
+//
+//  ALTConnection.h
+//  AltKit
+//
+//  Created by Riley Testut on 6/1/20.
+//  Copyright © 2020 Riley Testut. All rights reserved.
+//
+
+#import <Foundation/Foundation.h>
+
+NS_ASSUME_NONNULL_BEGIN
+
+NS_SWIFT_NAME(Connection)
+@protocol ALTConnection <NSObject>
+
+- (void)sendData:(NSData *)data completionHandler:(void (^)(BOOL, NSError * _Nullable))completionHandler NS_REFINED_FOR_SWIFT;
+- (void)receiveDataWithExpectedSize:(NSInteger)expectedSize completionHandler:(void (^)(NSData * _Nullable, NSError * _Nullable))completionHandler NS_SWIFT_NAME(__receiveData(expectedSize:completionHandler:));
+
+- (void)disconnect;
+
+@end
+
+NS_ASSUME_NONNULL_END