SCI: Add a new configuration option for SQ4 CD, "silver_cursors"

This allows the user to choose the alternate set of silver mouse cursors
that is available in the game resources of the game, instead of the
original golden ones

engines/sci/sci.cpp

@@ -194,6 +194,7 @@ Common::Error SciEngine::run() {
 	ConfMan.registerDefault("sci_originalsaveload", "false");
 	ConfMan.registerDefault("native_fb01", "false");
 	ConfMan.registerDefault("windows_cursors", "false");	// Windows cursors for KQ6 Windows
+	ConfMan.registerDefault("silver_cursors", "false");	// Silver cursors for SQ4 CD
 
 	_resMan = new ResourceManager();
 	assert(_resMan);