Adding more classes (including support for config-based facet groups)

This is related to https://github.com/GigaOM/legacy-pro/issues/4155, but doesn't need to wait for the actual styling to get pushed.

Done with @Camwyn
This seems suspicious. The facets have a name specified by the facet class file. Taxonomy facets have the added complication of possibly having different facet names from their taxonomy name. Why add yet another complication that the title class can be different from the facet name?