[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.
One of the downfalls of the lack of setTimeout management (see #1010) is this timeout needs to be cleared in any module that makes use of this mixin. See https://github.com/mozilla/fxa-content-server/blob/issue-977-expired-verification-link/app/scripts/views/confirm.js#L27-L29