Centralize data type color definitions

We have a color convention for data types (gene, protein, etc.) that's fairly fragmented in the Less sources. This makes it very troublesome to add new colors or modify existing ones, while keeping it consistent in all places. We should remove all duplicates and collect the color definitions in one place. There are multiple approaches to this, including defining them as a UI component, or perhaps using CSS vars.

*Update: We should also add more colors for the classes that are currently gray, e.g. CDNAClone, DOterm, RNAiScreen. One idea could be to make the colours automatically generated for the less used classes.*

Start by locating the Less sources containing the fragmented data-type color definitions and inventory their duplicates. Centralize the definitions, remove duplicate values, and add distinct colors for currently gray classes such as CDNAClone, DOterm, and RNAiScreen. Done means all affected UI uses one consistent source of definitions.

Written by the indexing model from the issue text.