Update with changes suggested by @nchapman and @zaach.

* Clean up Relier creation.
* Remove the "isSync" from the context of views that do not need it.
* Add a `Base` Relier that can be used as the base for other reliers or as a Null relier.
* Always pass in a translator into the FxDesktopRelier.
* Always pass in an OAuthClient to the OAuthRelier.
* Always fetch the webChannelId from the relier instead of ad-hoc.
* in fxa-client, ditch the relierHas and relierGet functions.
* Correctly set the default values in the models.
feat(client): Seemless verification in a second browser.

* Create a `resume` token from OAuth parameters. Pass it along to the fxa-js-client.
* Re-populate OAuth parameters from resume token on email verification.
* Bump fxa-js-client to 0.1.25 with the new `resume` hotness.
* Add functional tests for verifying in a second browser.
* Only show the serviceName in the ready screen if the user can continue with the OAuth flow.

issue #1623