Resolve colorblindness issues - PROBABLY add hatching - texture and viridis scaling

[wendlingd]

Good advice regarding color-blindness - use hatching, as described at http://lea.verou.me/css3patterns/#diagonal-stripes

See http://stackoverflow.com/questions/42705705/shaded-interactive-d3-treemap-support-for-people-who-are-colorblind.

Instead of green, consider http://lea.verou.me/css3patterns/#waves

Instead of shades of red, use d3.interpolateViridis(t), see https://github.com/d3/d3-scale

[wendlingd]

The problem with this is that the smallest boxes, which might be 1/4 of the total box count, don't manifest hatching in an understandable way. I think an accompanying data table might be the best solution.