config: get cat names from their general subcats

Except in one pointless case, category names are identical to the names of their 'general' subcats. If we fix that one case, as done here, we can remove the name attributes from the category table and instead fetch the name labels from the subcat table via general-subcat lookup, as done here.

The one case that had to be fixed for this to go ahead was the advanced category. The tree node had the label "Advanced" while the panel title had "Advanced settings". This inconsistency is unnecessary, especially since the help text displayed underneath the panel title says "Advanced settings".