Adds new images for release, beta and canary builds (both retina and normal)

Fixes #1117.

Retina:
![ember js - builds 2013-12-02 23-09-13](https://f.cloud.github.com/assets/1131196/1661061/ac1ad84a-5bd0-11e3-879b-5d97dca2ca8c.jpg)

/cc @wifelette @stefanpenner