Add fields to pledge form, and subscribe people who pledge (opt-out).

Adds email, first and last name, and an option to sign up for
email. The frontend sends a superset of everything it sent before, and
the backend expects, but doesn't require the new fields, so there
(hopefully) shouldn't be any cutover issues.
Be a bit more conservative during the cutover
Merge branch 'master' into mailchimp

Conflicts:
	backend/main.py
	markup/pledge.jade
Fix test include path
Remove the first and last name fields, and instead, split them based
on the full name we get from stripe. Hacky, I know, but it'll do.
Merge branch 'mailchimp'