AppRTC: Use WebSockets instead of Channel API.

With this change no messages are stored on GAE. Instead, they are stored on Collider.
GAE still keeps track of which users are connected to a given room.
Note that loopback will no longer work.
Ah misunderstood what you were saying - I'm good with just checking channelReady for sending message. I thought you meant the optimization where we don't wait for channel to be ready before starting peer connection.