Allow users to change their profile email

[marcoacierno]

We should allow users to change the email of their account via UI, without having to contact us via email.

### Tasks
- [ ] Add new flag to User to indicate if their email is verified or not
- [ ] Implement endpoint to send an email to verify their email address
- [ ] Add banner in UI asking people to verify their current email address
- [ ] Implement endpoint to trigger the email change flow
- [ ] Implement UI to change the email address
- [ ] Implement endpoint to confirm the email change, update the user email and orders to match their new email (?)