feat(client): Add the iframe flow.

* window.history.pushState is not available inside of an iframe. When FxA loads in an iframe, fall back to using the hash change event. If in an iframe, copy the pathname to the hash on startup.
* Add the oauth_iframe tests to the list of functional tests.

issue #1386
Update the "Channel timeout" string to be "Unexpected Error". Fix the web channel unit tests.
Use a cross-browser solution to parse the parent origin's URL.

Create an anchor tag, set the href to the relier's redirectURI, and fetch anchor.origin.
Use SASS variables for the fox-logo and close-button zindex values.
Merge pull request #1796 from mozilla/issue-1386-iframed-oauth

Issue 1386 iframed oauth flow