Interaction with MailChimp

[Nokel81]

The promotion's director uses MailChimp to send out promotional emails. Who is on that list should be synced with the settings on the server. The following needs to be done:

1. Everytime the promotional emails setting on the website is changed the user's email should be correspondingly added/removed from the mailchimp list through its API
2. Every {peroid} of time (say every hour) all the mailchimp emails should be gotten and the settings should be updated