Hi @AlbericoD,
Thanks for help. Finally got it solved and able to deploy my first extension on my channel. 
Don’t know what was the cause of problem. But I solved it by taking following steps:-
- Taking git pull of Developer Rig Repo.
- Clearing my browser cache including cookies and local storage. And re-login to twitch.
- Running Rig app again as I was doing previously for online mode.
Though I still see my console full of errors esp., this one
Failed to load https://client-event-reporter.twitch.tv/v1/stats: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'https://localhost.rig.twitch.tv:3000' is therefore not allowed access.
This error comes even when no extension is loaded in my developer rig.
One more thing, I’m still not able to figure out the purpose of “OAuth Redirect URI” in Settings - Client Configuration in my extension on dev.twitch.tv .