Channels-yroom

- Restructure `yroom` worker to be not ASGI based
- Add improved exception handling to `yroom` worker:
- exceptions are now detected, logged and worker gracefully shut down

- Add setting to disable pipelining of messages for TipTap integration
- Fix bug where missing connect message would reset room
- Use existing Websocket consumer channel for communication from `yroom` worker. Before an extra channel was used.

- Fix bad worker configuration

- Change `YroomDocument` export API:
- Replace `get_*` with `export_*`
- Raise `DataUnavailable` instead of returning `None`
- Change `YroomConsumer` API:
- Change `get_room_group_name` to `get_room_name`
- Change settings to use `YROOM_SETTINGS` with per room-prefix settings