Mailchimp updates for auto sub/unsub

- RegistratonResponseMaker now records communication preferences on
signup
- UserPreferenceResponseMaker handles opt ins and opt outs of
communication preferences
- NewsletterList updated commenting, try/catch for unsub
- UserRepository commenting. Conditional removal of comms prefs
- New BroadCastResponder to handle unsubscribes and subscribes centrally
- UserBroadcastOrganiser now processes opt in and outs and returns an
object containing arrays of both
Merge branch 'article-endpoint' into dev