Add exchange BW

[bmancini55]

Exchange API URL
https://github.com/bw-exchange/api_docs_en/wiki
https://github.com/bw-exchange/api_docs_en/wiki/WebSocket-API-Subscribe-instructions
https://github.com/bw-exchange/api_docs_en/wiki/WebSocket-API-Reference

Additional information about Websocket connection
Supports tickers, trades, and L2 orderbook with an initial snapshot.

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Refer to Contributing Guide for additional information.

[HalcyonLA]

@bmancini55
Investigated this, and getting errors like this below:

{dataType:"90_TRADE_BTC_USDT",dataSize:20,action:"ADD"}
<< { msg: 'data not exist', code: '5016', dataType: '90_TRADE_BTC_USDT' }

The same with Ticker.

l2update works - should we implement it?

[bmancini55]

Dev notes:

• Connect to non-mainland china url: wss://kline.bw.com/websocket
• Prior to connection load a list of market_ids from https://www.bw.com/exchange/config/controller/website/marketcontroller/getByWebId
• Supports candles (refer to https://github.com/bw-exchange/api_docs_en/wiki/WebSocket-API-Reference#subscribe-kline-data-marketid_kline_klinetype_symbol)
• Supports l2 updates with an initial l2 snapshot (refer to https://github.com/bw-exchange/api_docs_en/wiki/WebSocket-API-Reference#subscribe-to-market-depth-data-marketid_entrust_add_symbol)
• Supports trades (refer to https://github.com/bw-exchange/api_docs_en/wiki/WebSocket-API-Reference#subscribe-trade-detail-data-marketid_trade_symbol)
• Supports tickers (refer to https://github.com/bw-exchange/api_docs_en/wiki/WebSocket-API-Reference#subscribe-tickers-data-all_trade_statistic_24h)