WIP Remove d3 dependency

Part of #1510 but I could do with some help from someone that knows how the original code was supposed to work.

- [x] Remove `_colorize`.
- [ ] Rework `@html` template to use just html.
That's because they are different. There is a stop for each end of the bucket and the stops are used for the gradient. The buckets are between the stops. The original code used `@index.forEach` to get the tab data while you're using `$.map stopData`.