Adding facebook to registration template.
Adding facebook SDK as a dependency.

For our social login support!
Redirecting the user to the FACEBOOK_LOGIN_URL setting.
Adding a Facebook login endpoint.

This will transparently handle the hard parts of social login by allowing
Stormpath to do the heavy lifting behind the scenes.
Adding a default facebook login URL (/facebook).
Adding a facebook_login view.

This view will grab a newly logged in Facebook user's access token, then pull
down their account from stormpath and log it in properly.

This makes it possible to use normal stormpath permission / etc. stuff --
without breaking anything!
Adding a User.from_facebook() method.

This allows us to create a new Account given a Facebook user's access token.