Update nodejs demos

I've taken the liberty of trying to update the nodejs demos in this repo to work with the new google-api-nodejs-client. I haven't actually tested the changes so if someone could give this a second look & perhaps test it, that'd be awesome.

Plus general feedback is always welcome. Maybe we want to scrap this altogether and create a better demo?
Do you have something like `.withDefaultParam` that you could use on the client to avoid passing `datasetId` on each API call?