Return token as JSON, remove Room from grant

[jandusek]

In order for the Video Quickstart JS to be able to process the token, it needs to be returned as a JSON.

[ceaglest]

As far as I know all of the token servers return the same format - a raw text body. Please don't merge a change unless its coordinated with the other dependencies of this project:

https://github.com/twilio/video-quickstart-swift
https://github.com/twilio/video-quickstart-objc
https://github.com/twilio/video-quickstart-android

As well as all of the other example servers.

[jandusek]

The Node.js quickstart's /token returns JSON:
https://github.com/twilio/video-quickstart-js/blob/master/server/index.js#L73-L76

And the JS client expects JSON:
https://github.com/twilio/video-quickstart-js/blob/master/quickstart/src/index.js#L43

Good point about the other dependencies, I'm not sure what format those need.

But this should probably be unified one way or the other.