Add Typetalk OAuth2 support

In my opinion, skinny's OAuth2 module should have lots of out-of-the-box OAuth provider support.

Typetalk is a realtime instant messaging service from @nulab. http://www.typetalk.in/
Thanks to Nulabbers, I just tried to create OAuth 2 integration feature with Typetalk API yesterday. http://www.zusaar.com/event/8747007