Add category breadcrumbs to edit category page (PR #13126)

Currently, there is no easy way to switch between categories when editing one. This fixes that.

GitHub

This looks OK to me.

I do wonder whether it’s a bit of a power-user feature that can potentially confuse novice users. (A user could be editing category A, _not_saving changes, then switching to category B, and wondering why category A changes weren’t saved…)

@pmusaraj I wonder if we merge this now and see if anyone complains. If they do, we can disable the dropdown when there are unsaved changes. We can grey out the dropdown with some text explaining there are unsaved changes. But I don’t want to do that work if it’s not a real issue.