Recreate Advanced Forum's forum list display

WIP - a view that rebuilds the display.

For anyone using the Barrio Bootstrap theme, you might find the forum top category display is displayed at the bottom of the theme instead of the top, it's because of an odd choice in Bootstrap; see 🐛 Table captions should be at the top Active for details.

It makes more sense for it to be "forum categories", not "forum, topics".

Thanks, I tried the patch, but get a "No forum categories were found." under /forum, even though there are two fora.

The forum structure was built to require that forum categories fit inside a forum container. In practical terms, it means you have to build a hierarchical forum vocabulary.

There's probably a better way of doing this, but this was sufficient for our needs.

Thanks @DamienMcKenna - can we get an MR so we can have gitlab CI? There's no drupalci here anymore

Thanks for clarifying @DamienMcKenna -- with fora inside containers it works fine. Shouldn't we require containers, if they are in actuality required?

There are probably better ways of building the display, this was more of a proof of concept that worked for a specific project I'm doing (site migration from D7) rather than a finished change.