Support changing the listed email on your profile

[mrchrisadams]

The email listed for a user usually comes from their slack account.

This serves multiple roles.

1. it acts as a key for lookups when importing information about a user
2. it acts as a way to be contacted if a user chooses to be contacted
3. it acts as the way to log in when following the email sign-in flow

Because it serves multiple purposes, it's important for this email to be a genuine one, as well as something the user has control over making visible.

This issue pertains mainly to supporting the updating and listing of a verified email address.