Facebook login

Adds Facebook login through JS popup flow

![screen shot 2013-09-06 at 11 26 49 am](https://f.cloud.github.com/assets/4422080/1097430/3abf8ef6-1711-11e3-9e1b-e831bf04974b.png)

![screen shot 2013-09-06 at 11 28 14 am](https://f.cloud.github.com/assets/4422080/1097453/624d2000-1711-11e3-92a4-429abd6e3482.png)

![screen shot 2013-09-06 at 11 29 05 am](https://f.cloud.github.com/assets/4422080/1097469/7a63bcb2-1711-11e3-94db-1c47bc9b2b7e.png)