feat(client): Password reset email prefill & /force_auth simplification.

* Prefill email address from query string on `/reset_password`.
* If a user clicks "forgot password?" from `/force_auth`, skip `/reset_password` and go directly to `/confirm_reset_password`.

Closes #549
Closes #637
Merge pull request #659 from mozilla/issue-637-reset-password-email

feat(client): Password reset email prefill & /force_auth simplification.