Add user.updateEmail() and user.updatePhoneNumber() methods

[tyrw]

We want a logged in user to be able to update their own email and/or phoneNumber via Core JS.

// Should send an verify link by email
Userfront.user.updateEmail(email);

// Should send a verification code by SMS
Userfront.user.updatePhoneNumber(phoneNumber);

These methods should call the verify an email and verify a phone number endpoints, respectively.

Post-deploy tasks

• [ ] Notify the admin (convo 410)