refactor(client): Move many parameters/helpers from Session to Relier.

@nchapman and @zaach - this is part one in the ["resume" PR](https://github.com/mozilla/fxa-content-server/issues/1623). The PR became pretty burly, so I factored out this portion, and will issue a follow on PR with the resume functionality.

--------------------------------------
 
parameters:

* service
* most oauth parameters
* redirectTo
* context

helper functions:

* isSync
* isFxDesktop

Other work:

* Split of the OAuthRelier from the normal Relier
* Initialize Channels with the Relier in app-start
* Update the oauth-reset-password functional test to not hard code the email format. Instead fetch the link from the email headers.

Remove all of the resume stuff.

issue #1648
I'm confused. We added `underscore`, but I don't see it used below in the diff.
Oddly, running `grunt lint` passes, so either I'm missing something, or maybe JSHint isn't checking for unused vars (which may be true since it's kind of an unused argument in this case).