attendee newsletter CSV export

creates a CSV file that is ready to import into MadMimi (and probably other providers) of attendees who want to sign up for the newsletter

at some future point I will also do this with staff newsletter people as well.

need Eli's eyes on this before merge, appears to work correctly on my machine.
Ok will fix

Madmimi doesn't need zip but... eventually might have something where we have a west coast specific mailing list that gives more frequent updates to people that would care about hearing more often of west coast stuff