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
I thought this would have been done as part of https://github.com/mozilla/fxa-content-server/pull/1645/files#diff-b80f22cfd726dfdc2bb7ed3e82dc7264R122.