Remove deactivated accounts from mailman

Everything in here only applies if mailman is in use.

Previously, we did not attempt to remove users from mailman lists if they deactivated their account, nor did we change their email address if it was changed.  Now, we will do so.  In the case where the user has multiple accounts, this gets tricky.  If they change their email, we keep both emails.  If they deactivate their account, we deactivate all other accounts with the same email address.  (The page warns that this will happen.)

This also adds a script to update existing lists.  This is a bit difficult as we don't know how they got the way they are, so the script is a bit cautious.

Unfortunately, this is somewhat untested since I don't have a local mailman install.  I will do some manual testing when I put it on esp.mit.edu, and I think that is the only site that uses mailman.

Fixes #132 and #664.
Good catch.  I think the right thing to do here might be to only subscribe them to lists that make sense for their account type.  (So this would be announcements@ for parents, teachers@ and class-teachers@ for teachers, anything except teachers@ and class-teachers@ for students, and anything for admins.)

I also realized that this will apply to any manually-created lists, and I'm not sure if that's a good idea or a bad one.  (We don't use them much, but we do use them, e.g. for student reps.)  I'm thinking the right behavior is to change the address in all of them; the only cases where this might not be correct are admins and we can deal, but it's worth thinking it through further.