Websocket refactoring to chanx

[robinharms]

• Subscribe to participants/meeting at once, and then dispatch a job to fetch required app_struct.
• The channel class from envelope isn't needed if we use mixins from chanx directly for broadcast.
• Replace the connection object with some other kind of class and migrate. Use async methods to update?
• Status and id for some messages needed.
• Make sure batching works as expected. (Basically on transaction commit)

Extra:

• Is it possible to have a shutdown-functionality to allow graceful shutdown?
• Semaphore for incoming messages, especially heavy ops.