CaseIH 1660 and 1680 v1.0

Here is my edit of the ingame CaseIH 1660 to an American version. You have a choice of the older Navistar DT-466 or the newer Cummins 8.7L engine and the ability to configure a 3ft longer auger for wider headers. I've created a new ladder for the cab, door for the ladder in the rear, rubber skirt for the straw chopper, and new decals to cover the engine and model version.