Pull request for chemistry module!

Hello!

I've finished integrating my chemistry mod into AITS, along with adding a few new features here and there:

IAITSModule now has a registerItems() method.
CommonProxy now has an Enum of all the textures to preload, ClientProxy iterates over it; this minimises the number of times code needs to be edited.

Changed all shiftedIndex's to itemID's... I think those still using shiftedIndex need to update MCP...