Use Serializer to serialize message in websocket consumer's chat message response.

[gibsonbailey]

Currently, the data broadcasted through the websocket when it receives a chat message is a hard-coded dict. This should probably be controlled by a configurable serializer.

Current code in consumers.py

[gibsonbailey]

It could be good to look into profiling on the consumer to check how much it's costing us to use DRF serializers rather than a simple, explicit callable.