OAuth2

This implements OAuth2 using stuki/oauth2-simple-client new Meetup client.  The client is authenticated with Zend auth with a custom auth adapter.  A $serviceManager->get('MeetupClient') returns a custom dms/meetup-api-client object to use OAuth2 (it didn't before).

ZfcUser and scnSocialAuth were not used because the mechanism scnSocialAuth uses requires you to _copy_ files from one location into another in the project with no means to specify an adapter outside the project.  It's a ZF1 legacy solution.