[wip] Issue 977 expired verification link

We're not able to have a resend verification link in all cases. It's only possible to resend the email if you have the `sessionToken`, which is only available in the browser you signed up with. Should we keep it that way or remove it altogether?

cc @pdehaan @shane-tomlinson 

Fixes #977.
To make sure, `UNKNOWN_ACCOUNT` means the link is expired, and `INVALID_VERIFICATION_CODE` means the link is damaged?