WIP: Start on an OAuth RP include.js with a promises based API.

* Add an IFRAME channel that has the ability to communicate back to the parent window.

issue #1386
Not sure if we want/need a fallback for browsers which don't support `rgba()` (which according to http://caniuse.com/#search=rgba may just be IE8).

#PROTIP: click on the "Usage relative" button on http://caniuse.com/#search=rgba and it shows an awesome stacked chart of browser adoption/usage!