feat(client): Forward the `resume` token to the auth server

This build on #1645 and should be reviewed afterwards.

* `resume` is imported from the URL and stored in the Relier.
* fxa-client sends the token to the auth server in `signUp`, `signUpResend`, `passwordReset`, and `passwordResetResend`

issue #1623
The relier was not previously used by the FxaClient, so I incorrectly did more setup work to create a relier to pass into the fxa-client in #1645 than I needed to.