Add color brewer as source for all colors in Emperor 

Using chroma we are able to interpolate over all the color brewer colormaps, these are shown on the GUI via a drop-down menu (see animated gif below).

![colors](https://cloud.githubusercontent.com/assets/375307/4429710/c9fdb546-45fc-11e4-8427-a9e3d6995754.gif)

Discrete colors are all now as provided by the divergent list of colors in color brewer, I don't think these are the best colors, but it's what we had decided in the two issues where we discussed this.

The code to generate the color list was moved to the library in util.js and its dependency on THREE.Color has been removed (this was unnecessary).

@lkursell, @JWDebelius, @wasade, your input would be very useful.

Fixes #299 and #161.