Updating plug, moving redirect_uri to Strategy, adding support for other params

Expires_at -> expires_in (https://tools.ietf.org/html/draft-ietf-oauth-v2-31#appendix-A.14)  
other_params: some oauth services add other params (Facebook, for example, adds `machine_id` : https://developers.facebook.com/docs/facebook-login/access-tokens)
So, I'm not sure this change makes sense. The response gives us an `expires_at` as a number of seconds. We're taking that and turning it into a timestamp. So `expires_at` makes more sense to me.