Embeddable badges

For @jolankester to look at.

When someone clicks to embed the certificate, they see:

![popup](https://f.cloud.github.com/assets/395050/636604/e52c5ec8-d288-11e2-9ef9-52d2f70c797d.jpg)

The badge operates like the badge will on the site itself, so if you hover over it you get details about the certificate popping up:

![onhover](https://f.cloud.github.com/assets/395050/636607/f8079cb0-d288-11e2-8aa4-f5054389f845.jpg)

This is the styling that Adrian suggested. Let me know if there are any other changes you'd suggest.