Add a way to retrieve extra data received with token

Bungie API when returning the OAuth2 token also send some extra data like the membership id of the logged in user. In the current state, the data is discarded in QOAuth2AuthorizationCodeFlowPrivate::_q_accessTokenRequestFinished().

The current solution is to override QOAuthOobReplyHandler::networkReplyFinished(QNetworkReply *reply). This is a bit ugly because the override code will be the same except for the 2 lines required to extract the value.