Added config GUI system

Here are a few images of the FML Sample GUI:
http://imgur.com/a/3gQXp

This PR includes all the classes that are involved in building and displaying the GUIs. The Forge PR contains the code to link up the Forge Configuration classes to the GUI classes using IConfigElement.

See also: https://github.com/MinecraftForge/MinecraftForge/pull/1114