Add Option Chain WebSocket Support

[git-saaran]

Please add option chain websocket.. I am forced to rely on polling to get updates.

[katmakhan]

Try directly subscribing to option chains symbol , via subscribe method?

1. Get the option chain symbol names by
   niftydata = {
   "symbol":"NSE:NIFTYBANK-INDEX",
   "strikecount":15,
   "timestamp": ""
   }

response_nifty = fyers_model.optionchain(data=niftydata);

2. Then subscribe to those symbols, via normal websocket method.