Adds in 'Mailman' steps

This addition includes steps to (a) add new person to Mailman lists, and the step to remove them, before bounce processing does ;)

I'm advocating using remove_members, not find_members, so things can be done in one step -- invoke remove_members without any argumements to see its options -- in somecases no notification might be sensible.

We may also want to run `list_owners -wm foo@example.com`, to check for owners/moderators.
Shall I do another PR? Or just edit?