Mailchimp integration: solve problem of urbanmosaic using non-default address format

[wipascal]

Urbanmosaic does not use the postal-address fields of Mailchimp, but uses their own custom fields.

Ideally Urbanmosaic would change their way of representing addresses.

We can try to implement a work around in our code, but the Problem is that UM uses a text field for the country. That means that the user can enter an invalid country and our code wouldn't know how to deal with that.