Add 'access_type' to GoogleOauth2 optionalUrlParams

- If your application needs offline access to a Google API,
- then the request for an authorization code should include the access_type parameter,
- where the value of that parameter is offline
- ref https://developers.google.com/accounts/docs/OAuth2WebServer#offline
- Added test.
Merge branch 'master' of github.com:anilmaurya/torii