Tightly couple django and mailman

Issue #25 (closed) implements the old API that gets called in a cronjob, firing a Python script that talks to it over HTTPS. We could replace this:

• either by a cronjob Python script that queries the database directly
• or by a save() handler that updates mailman when MailingList changes
• or at the very least by a more nicely separated API with less GET variables (i.e. not one url route)