Sofa / Comfychair update

* Made sofas colorable by RGB rather than fixed onto the icon. Colors can be set by mappers with the color var, or by using the traditional object children (sofa/teal, sofa/brown, etc). Ingame color changing will be for some other PR.
For mappers: Sofa types are still the same, they all look like grey sofas in-editor but will have their correct colors ingame.

* Made sofa's armrest be ontop of mobs buckled to the sofa
![fart](https://cloud.githubusercontent.com/assets/2332094/2668253/55c0d4d0-c0b7-11e3-857f-594e99e6cdd5.gif)