Email Address Relationship

[drewroberts]

With the creation of the new Email Addresses model (TIPOFF/authorization#57), all string fields for email in this package should be replaced with a findOrCreate() relationship with that model. We can use the app('email_address') & nova('email_address') helpers added in release 1.8.3 of tipoff/support.

In addition to changing the database migrations, we should also update the model, factory, and nova resource. Later, we will have a custom nova field (TIPOFF/authorization#59) for our usage of Email Address.