Clean up gateway_hub implementation

[piyushk]

While introducing the hub sidekick and connection statistics, I've made a bit of a mess of the gateway_hub implementation.

[piyushk]

Need to work on this issue once #221 gets pulled in, as I wanted to split cleaning up in a separate pull request.

• Learn how to make these lists
• Move named_gateway functions to rocon_hub_client. All the named_gateway functions should uniformly use the gateway_name instead of key.
• Check if parsing functions are really needed. If needed, move them to rocon_hub_client. Should probably look more closely at the pyredis code.
• Modify all the connection statistics set and get functions to use pipelines. Save on number of individual requests.
• Get hub sidekick to use rocon_hub_client instead of gateway_hub.

[piyushk]

Since this issue is non-essential, I will get back to it once the demo is over.