configitems: allow for the registration of "generic" config item
Some section can contains arbitrary keys (eg: color, alias, extensions). We
add a way to register some generic config items for them. This is necessary to
get all the config registered. We use a regular expression because some sub-
attributes (eg: hooks.xxx.priority) can define default value on their own.
public attributes not in abstract interface: badpeer.badattribute
public attributes not in abstract interface: badpeer.badmethod