Find a better replacement for StyleC

[japgolly]

The StyleC experiment was meant to address the following:

1. A logical/composite style (eg a style for an entire widget) can have multiple CSS styles that need to be applied.
2. Adding a new sub-style to a composite style should result in a compilation error in all places that you don't update to use the new sub-style.
3. Styles all have the same type. Adding/removing/reordering sub-styles shouldn't result in silent undetectable errors where the sub-style ends up being applied to the wrong part of HTML.

StyleC does actually solve those things. It's just a horrible pain in the ass to use. Anyway, a replacement will need to at least consider the above goals with the additional goal that it not be horrible to use.