Figure out how to deal with the Unit/LayoutConfig.Unit collision

[CoryDCode]

Currently, LayoutConfigUnit is typedef'd as Unit. Unit is a foundation class (https://developer.apple.com/reference/foundation/unit), but only available in 10.0. It might serve the purpose we want, ironically, but we can't use it directly easily, because we support 8+. So we need to rename LayoutConfig.Unit, or something.