WebRTC Javadoc

Hi Philippe,

I've re-added and edited your Javadoc for the chat-video portlet. Could you review my edits and verify that they say what you intended?

I know there's been a lot of changes to these classes since you originally added the Javadoc, so I want to make sure this Javadoc is accurate based on the portlet's current state.

Feel free to send me a pull request with updates to the Javadoc, if necessary.

Thanks!