Websockets - synchronize with and subscribe to servers

[joepio]

See atomicdata-dev/atomic-data-docs#61

• When a client connects to an Atomic Server, subscribe using the /ws endpoint.
• When a Component subscribes to a Resource, subscribe to that through the websocket
• When there are no more localSubscribers to a Resource (no more components / hooks using the data), unsubscribe through the websocket.
• If the Server sends a Commit, process it
• Allow for multiple websockets (since it should be possible to receive updates from multiple domains / servers). Probably store the WebSockets in the Store as a HashMap / Map.
• Add e2e test for live updates

I think we can use the existing Store.subscribers map, which keys represent the subjects that should be subscribed in the websocket.

[joepio]