Email search opt in

We typically have a method like this be `get_contact_info` instead of `set_contact_info`, e.g.:

https://github.com/openstax/accounts/search?utf8=%E2%9C%93&q=before_filter+%3Aget

`set_contact_info` sounds like you are mutating a contact info, when you are really just retrieving it for use.