Improve the Mailchimp integration

The Bloomerang-Mailchimp integration should be improved so that information can flow freely back and forth in real time between the two platforms, allowing nonprofits to see all the communications their supporters are receiving in one place (their Bloomerang timeline).

When a supporter receives an email from Mailchimp, that should be automatically logged as an interaction in Bloomerang.

When a supporter opens or clicks an email from Mailchimp, that should also be automatically logged as part of the interaction in Bloomerang.

All activity taking place in Mailchimp should be used in the donor engagement score.

Bloomerang constituents should be automatically synced over to Mailchimp in real time, with custom field mapping. There should be nothing manual about the process.

At the moment, it's impossible to set this up via Zapier -- an individual receiving a mass email newsletter is not a trigger in Zapier, and even if it were, it would be cost prohibitive to run 9,000+ individual Zaps to create 9,000+ Bloomerang interactions every time we send an email to 9,000+ people.