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)
I'm fine with this change. I had this field in the struct at some point in the history, but decided to removed it for some reason.