Refactor new macOS code to reduce #ifs, increase shared code, and fix warnings

Limelight/OSPortabilityDefs.h

@@ -0,0 +1,24 @@
+//
+//  OSPortabilityDefs.h
+//  Moonlight
+//
+//  Created by Cameron Gutman on 3/26/18.
+//  Copyright © 2018 Moonlight Stream. All rights reserved.
+//
+
+#ifndef OSPortabilityDefs_h
+#define OSPortabilityDefs_h
+
+#if TARGET_OS_IPHONE
+#define OSImage UIImage
+#define OSColor UIColor
+#define OSView UIView
+#define OSApplication UIApplication
+#else
+#define OSImage NSImage
+#define OSColor NSColor
+#define OSView NSView
+#define OSApplication NSApplication
+#endif
+
+#endif /* OSPortabilityDefs_h */