manual sharing of badges on Facebook using opengraph

Manual sharing of badges already works on a fork I have of the backpack -- these are the steps to basically put these in sync with the recent backpack changes and share a pull request:

- [ ] add a Facebook share button to the modal, similar to Ocupop's mocks
- [x] embed opengraph data on individual badge pages (piece of cake once #499 is completed)
- [ ] add javascript for pushing badges to FB, likely added to share.js (already written, but may require some cleanup)
- [ ] add ability for users to attach a comment/message to their badges when they are shared

Reference facebook diagram: 
![Screen Shot 2013-02-16 at 3 16 59 PM](https://f.cloud.github.com/assets/1424627/164286/6a8be47a-788f-11e2-8a9c-8ceca376fbec.png)

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