Add-ons for Australis contest promotion (bug 979731)

https://bugzilla.mozilla.org/show_bug.cgi?id=979731

- Waiting for expanded image to fit the discovery pane
- Waiting on fonts information, I've guessed one but don't know about the other

**Screenshots:** (you can see the image is not quite right for the discovery pane on the second one):
![mainpromo](https://f.cloud.github.com/assets/187006/2334061/6845bf80-a474-11e3-9fb7-bc37188fd092.png)
![discoverypromo](https://f.cloud.github.com/assets/187006/2334062/68718d7c-a474-11e3-98d8-a5f4e14049fd.png)