Optional User Relationship

[drewroberts]

Contacts (#30) are created a null user_id. When the form is saved, the email field is used to check if the email address belongs to a User (TIPOFF/authorization#20) in the system. If it is, then the User is attached to the Contact.

There should also be a command in this package that can be run periodically to check the email addresses of Contacts with null user_id's to see if a user has since been created with that email. This command will attach the User.

[chx2]

Due to the new structure of EmailAddress in #46, the attach user command will need to be refactored to reflect this change.