config: rename advanced cat's general subcat for consistency

as just discussed in the previous commit, every cat has a 'general'
subcat, and for the 'advanced' category, it unusually uses the term
'misc' instead of 'general' in its name, which can cause confusion.

this fixes that name inconsistency, making it perfectly clear that
this is a 'general' subcat, and thus clarifying where options for
this subcat will show up, and where plugins targetting this subcat
will appear in the preferences tree.