Add Mailchimp API syncing.
Process email changes that are done via the inline edit form.

When an email is changed via the inline email edit form, the Contact edit
post hook is not run, so we have to do some extra work to process these
changes to see if a Mailchimp sync is necessary for the change.
Change the way we store interest groups from Mailchimp.

Mailchimp requires the interest group name rather than id to be used for API
requests, so we have to store the name. We're going to contine storing the id
and use that for the the group form as that is more reliable for that
purpose.
Add scheduled job for syncing from CiviCRM to Mailchimp.