feat(client): Allow the user to restart the signup flow on email bounce.

feat(client): Allow the user to restart the signup flow on email bounce.

Add two new error codes:
* 1018 - SIGNUP_EMAIL_BOUNCE
* 1019 - DIFFERENT_EMAIL_REQUIRED

fixes #1801
To clarify, you can load the settings page in a new tab (where `Session.uid` would be undefined) then try to change your password on an unverified account.