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

feat(client): Seamless verification in a second browser.

* Create a `resume` token from OAuth parameters. Pass it along to the fxa-js-client.
* Bump fxa-js-client to 0.1.25 with the new `resume` hotness.


issue #1623
why toResumeToken instead of getResumeToken? The entire state of the relier isn't being encapsulated in the resume token.