Don’t save empty email textfields as empty string emails on person object.
But if person already has an email and the field is now blank, treat that as intentionally deleting the email (251f95065403bd8afeca3d95c55ab97cca09769f).
Allows `initialUserEmailAddress` to be updated after sending the Feedback Form with no email.
Fixes IOS-415
Ability to delete a previously entered email
Fixes IOS-418