Updated the facebook login_from to allow logins using the Facebook JavaScript SDK

The login_from for Facebook now allows users to login using an access token directly instead of using the code parameter. This allows login via the Facebooj JS SDK (FB.login).

To easily integrate the client side behavior, you can just hijack the click on the facebook button like so (in CoffeeScript):

    # assumes that the Facebook JS SDK has been loaded beforehand
    $('#facebook-sign-in').on "click", (e) ->
      e.preventDefault()
      FB.login (response) ->
        window.location = "/auth/facebook/callback?access_token=#{response.authResponse.accessToken}&expires_in=#{response.authResponse.expiresIn}" if response.authResponse