Reduced the potency of carrying multiple light sources.

Modified how light levels are stored, and how items can adjust the player's luminosity.
Each light source on a player's person will still increase luminosity, but with diminishing returns.
This PR does not modify the brightness of any single object, but rather how they merge brightnesses.

![2014-02-05_16-31-34](https://f.cloud.github.com/assets/1637936/2092830/acaf8d10-8eb0-11e3-82e7-5f4047032757.png)