[Bug 939312] Australis Onboarding whatsnew testing for Aurora and Beta users

This is the first iteration of the Australis browser UITour, which is going out to Aurora users (en-US only at first) on Mac OSX and Windows (note: Linux users will not get the tour this time round).

To test:

* Please use the latest up-do-date Firefox Nightly (today's build).
* To enable the tour to run locally create the following preferences in `about:config`

1). `browser.uitour.requireSecure` (type: boolean, value: false)
2.) `browser.uitour.whitelist.add.testing` (type: string, value: `http://127.0.0.1:8000`)
3.) Then restart the browser

Still waiting on one possible string change, but we can start review. This is due to go out by the end of today, Tuesday 4 Feb.

Note there is some conditional logic in the web page behind the tour. If the user goes through all four steps of the tour, they will get a different survey link and blue CTA button link on the post-tour web page.

Also `australis-uitour.js` is an externally maintained library located here: https://github.com/Unfocused/mozilla-uitour. This helper library has been written by Blair, one of the Firefox developers working on the UI interactions.