Bug: mailinglists mapping - private property handling is inconsistent

[sebbASF]

setup.py creates the mailinglists mapping with the properties: description, list, name

However archiver.py creates entries using the properties: description, list, name, private

Also edit-list.py stores entries using the properties: description, list, name

If the private property is useful, then setup and edit-list.py should take account of it.

It's not clear if the private property is useful when applied to a list, as each message has a private property. It might be best to just drop the property in archiver.py.