Add pipeline_publish_message method to redis_store

[mlindemu]

• Unit tests added to test_chatclient

[mkaluza]

Hi! I've stumbled upon a similar perf problem and came up with this: https://github.com/mkaluza/django-websocket-redis/tree/publisher_connection_override

Wouldn't this be simpler and more flexible? It allows you to publish many different messages with only one roundtrip instead of just one - you just pass the pipeline as connection.

And to mimic the functionality of your PR, I'd add a pipeline bool parameter to the constructor instead of adding a new method - that would make it easier to migrate existing applications to pipelines