Add mailchimp requirement.
Mailchimp integration config variable.
Mailchimp List.
PyBossa newsletter integration with Mailchimp.
Configure mailchimp newsletter.
Subscribe new users.
Template config vars for Mailchimp.
Subscribe also users from Google+ and Facebook.

Twitter does not provide email, so we'll handle it in another place.
New column to control newsletter subscription.
Show newsletter subscription to users.

Only when registering or when they've not seen the page before.
Show newsletter subscription if user has not been prompted.
Use newsletter template.
Show only newsletter view if enabled.
Show a 404 if newsletter is not configured.
Fix for newsletter.
Fix newsletter.
Use last version
Test newsletter.
Test.
Test.