[TRI-2388] Force verification when changing email address

[matt-aitken]

You can update your email address in your profile (when logged in). We don't verify the new email address.

Suggested fix

1. Users can request an email address change, but it is in a pending state. It keeps the old email until verified.
2. Once verified it switches to the new email.

This will require a new table in Postgres for when an email address is in progress. Or we could move to have multiple authentication methods for an account.

_TRI-2388

[Kiran-Alex]

Hey @matt-aitken , I would like to work on this issue. I guess there's no PR for this.