Add additional exchange support

[jzbz]

Currently we're only displaying order book depth metrics for Binance, Bittrex, and Poloniex. This tool can actually be quite useful for making decisions on where to trade as well as revealing exchanges that might be misbehaving.

In the event that a market maker is engaged it will also make monitoring that work much easier.

Exchanges that it would make sense to monitor:

Exchange	Cross	Link
OKCoin	DCR/USD	https://www.okcoin.com/spot/trade#product=dcr_usd
OKEx	DCR/USDT	https://www.okex.com/market?product=dcr_usdt
OKEx	DCR/BTC	https://www.okex.com/market?product=dcr_btc
Huobi Global	DCR/BTC	https://www.hbg.com/dcr_btc/exchange/
Huobi Global	DCR/USDT	https://www.hbg.com/dcr_usdt/exchange/
Huobi Global	DCR/ETH	https://www.hbg.com/dcr_eth/exchange/
Upbit	DCR/KRW	https://upbit.com/exchange?code=CRIX.UPBIT.KRW-DCR
Upbit	DCR/BTC	https://upbit.com/exchange?code=CRIX.UPBIT.BTC-DCR
CoinEx	DCR/BTC	https://www.coinex.com/trading?currency=btc&dest=dcr
CoinEx	DCR/BCH	https://www.coinex.com/trading?currency=bch&dest=dcr
BW.com	DCR/BTC	https://www.bw.com/trade/dcr_btc

[buck54321]

The problem with many of these exchanges is that they are suspected of wash trading. See

https://www.sec.gov/comments/sr-nysearca-2019-01/srnysearca201901-5574233-185408.pdf

and

https://www.sec.gov/comments/sr-nysearca-2019-01/srnysearca201901-5164833-183434.pdf

I'll try to list my current thinking on adding these.

Huobi Global is already implemented, but off by default because of suspected wash trading.

OKEx is suspected of wash trading.

OKCoin has low volume/poor liquidity.

Upbit is a capital-controlled market because South Korea. I don't know the full implications of this, but I do know that it makes arbitrage difficult and it was reason enough for link 1 above to disinclude Upbit from consideration in their report.

CoinEx is suspected of wash trading.

Not a lot of info on BW.com. Their trade histograms are represented in the first link above, but not explicitly discussed. My amateur analysis of the histograms says that they're wash trading.

[jzbz]

I'm aware all those exchanges are currently suspect. In most cases the "wash trading" isn't even that, they're so lazy they just make database entries to fake trade history instead of actually churning some coins and generating volume, in which case the order books will be empty. If we're potentially engaging market makers who will show $N per side, having a way to monitor them in one place is useful.

[RyanBRiley]

I'd like to take this on.