Use Command key instead of Control as modifier on macOS

This provides an experience closer to the original classic Mac version.

This is supported by the earlier changes to gracefully quit the game.

GpCommon/GpVOSEvent.h

@@ -97,8 +97,8 @@ namespace GpKeySpecials
 		kEnter,
 		kLeftShift,
 		kRightShift,
-		kLeftCtrl,
-		kRightCtrl,
+		kLeftCtrl,  // Maps to Command modifier on macOS.
+		kRightCtrl, //
 		kLeftAlt,
 		kRightAlt,
 		kNumLock,