Inventory slot system

This is an inventory system I'm creating. Here's a cool image to show you what I've accomplished so far:

Survival Mode:
![screen shot 2013-12-18 at 8 42 44 pm](https://f.cloud.github.com/assets/711973/1779604/69c1a9a2-684f-11e3-9046-ace7538bc38a.JPG)

Creative Mode:
![screen shot 2013-12-20 at 12 09 26 am](https://f.cloud.github.com/assets/711973/1788627/0304b100-6935-11e3-82af-5f17735fcf59.JPG)

Currently in development are a few more features (mining_crafting branch), seen here:
![screen shot yeah it finally took a screenshot whooo that took so long you guys have no clue](https://f.cloud.github.com/assets/711973/1797396/426f0a4e-6ad3-11e3-9f27-f17ae725a07b.jpg)
![screen shot i can has pickaxe](https://f.cloud.github.com/assets/711973/1799423/d33998e2-6b9a-11e3-8bf6-79c586ea50eb.JPG)


Keys 1-9 select the inventory slots, you can also scroll or press E to cycle. The selected slot determines which block you will place.

TODO: Allow item drop entities, mining?, crafting? etc.

@fogleman: You can probably merge this now, as it supports creative and generally works well.