Category tags

[ArtOfCode-]

In this PR:

• Categories now have 'required tags' and 'topic tags'
• Posts in a category with required tags must have at least one of those tags
• No such requirement for topic tags
• Both required and topic tags get special display: topic tags get an outline, required tags are filled.

[cellio]

Your description sounds good to me. I've been trying to think of a better way to talk about required tags (to users), because it's really that you must include one member of this set. Any individual tag in that set isn't required; it's that you have to choose one from the group. If I could come up with better language I'd want to use that in the UI (defining them, instructions to include one, error if you don't). If anyone has any ideas please share. If not we can go with this; I just have this nagging feeling...

Can we set this up on the dev server to poke at?

[ArtOfCode-]

Done. Dev server should be ready to poke.

[luap42]

Seems okay, but CI is failing. :)

[ArtOfCode-]

That's rubocop - I'm going to ignore it for now and fix it later on develop.