Use add facebook endpoint

- remove util/fb.js in favor of angular-facebook bower component
- refactor facebook-reward-controller's methods to promises
- connecting with facebook hits fb servers, /user/add_facebook, then claims

https://docs.google.com/a/stellar.org/document/d/1X0OEbNsvGMCXpKMU5NihawI6LOOjoe7R5L7ZqCD-kHs/edit