User prefs currently is a in-memmory store.

Should perhasp be a DB table which is just a user X json struct store.

There are some complications when putting json into the DB but as there's no user data I think it's a not too bad idea.

Or not a new table, but a injected field into the users table.

Would be also good to make sure there is a lock when reading / writing settings as to not loose data.