Refactor relative touch handling into a separate class

Limelight/Input/RelativeTouchHandler.h

@@ -0,0 +1,19 @@
+//
+//  RelativeTouchHandler.h
+//  Moonlight
+//
+//  Created by Cameron Gutman on 11/1/20.
+//  Copyright © 2020 Moonlight Game Streaming Project. All rights reserved.
+//
+
+#import <Foundation/Foundation.h>
+
+NS_ASSUME_NONNULL_BEGIN
+
+@interface RelativeTouchHandler : UIResponder
+
+-(id)initWithView:(UIView*)view;
+
+@end
+
+NS_ASSUME_NONNULL_END