Bubblegum

- Adds bubblegum to snack vending machine.
- ~~Bubblegum can be used to disable cameras~~, but doesn't give nutriments.
- To avoid the bubblegum's animation from clipping through helmets, I had to change how masks and helmets are drawn on humans. This shouldn't be visible, unless you give HIDEMASK or HEADCOVERSMOUTH flags to items that shouldn't have them.

![bubblegif](https://f.cloud.github.com/assets/5390315/1838094/30ecb0c4-7450-11e3-91a6-a288c662ae9b.gif)