Added GUI barebones and test item

The test item opens a basic GUI which currently just dims the screen.
Add the actual item and texture

Derp fix: forgot to commit the actual Item class and texture.
Register the item

Derp fix v2: Forgot the updated ModItems class
Register the GuiHandler

Derp fix v3 (wow, forgetful today): Update the Mod class to register the
IGuiHandler. Hopefully last derp fix for now.
Added basic refueler for grind stone and future use

The refueler will accept WhiteCraft fuel and fuel from mods which
implement an interface. (Hint: API)