Added support for new FML config GUI classes

Here are a few images of the config screens for Forge:
http://imgur.com/a/GXelz

This PR bridges the gap between the FML PR that adds the config GUI classes and the Forge Configuration classes used by many modders. It also adds config GUIs for the Forge config files.

See also: https://github.com/MinecraftForge/FML/pull/437