Better Colors

[curran]

Currently we're using d3.schemeCategory10, which only gives us 10 colors. Some colors are used for multiple countries.

I think it would be better if there were many discinct colors. It's not critical that we be able to distinguish between each one, but we'd like to at least have all countries appear to be different to each other in color when they are placed next to each other in the StreamGraph.

Here's an example of what we want to avoid (in red boxes):

[curran]

Some ideas:

• https://bl.ocks.org/mbostock/310c99e53880faec2434
• https://github.com/d3/d3-scale#scaleSequential
• https://github.com/d3/d3-scale#schemeCategory20

[curran]

Also lighter colors with dark text would be good, so we can have text over the bars for small displays - related to #93