Start the interactive add scopes flow. #397

-[GIDVerifyAccountDetail verifyAccountDetailsInteractivelyWithOptions:] takes in an instance of GIDSignInInternalOptions to start the interactive add scopes flow. This issue will be implemented in two parts:

1. Check to ensure that the client has passed in valid parameters, provided a valid presenting view controller, and defined the proper callback schemes at the moment,
2. Start the incremental authorization flow by creating an OIDAuthorizationRequest, similar to our interactive sign in flow