Share buttons

Merge pending https://github.com/guardian/frontend-admin/pull/106

- ~~Design work~~
- ~~It uses the desktop facebook app id. Is that ok?~~
- ~~A discussion about how we get the numbers against each share ([JS](https://github.com/dbushell/socialite) Vs [Server](http://sharedcount.com))~~ - later

![social](https://f.cloud.github.com/assets/84996/233277/ce888988-874e-11e2-9417-dad715398a7b.png)

![video](https://f.cloud.github.com/assets/84996/233306/84fdd6be-874f-11e2-90ed-474f2318b07d.png)