Feature/trade page url part b

[yihyang]

• What is the purpose of this Pull Request?

Adding missing trade_page_url for:

• [x] Bit-Z

• [ ] Bitbay : Unable to implement as bitbay uses full name for base currency -> https://bitbay.net/en/exchange-rate/ethereum-price-eur

• [ ] BitBNS: Unable to find the trade_page_url

• [x] Bitcoin Indonesia (Indodax)

• [x] Bitfinex

• [ ] Bitflyer: Unable to implement as bitflyer uses full name for base currency -> https://bitflyer.com/en-jp/bitcoin-chart

• [x] Bitforex: Unable to find the trade_page_url

• [ ] Bithumb: Unable to find the trade_page_url

• What is the related issue for this Pull Request (if this PR fixes issue, prepend with "Fixes" or "Closes")? https://github.com/coingecko/cryptoexchange/issues/991

• [x] I have added Specs

• [ ] (If implementing Market Ticker) I have verified that the volume refers to BASE

• [ ] (If implementing Market Ticker) I have verified that the base and target is assigned correctly

[tmlee]

sorry @yihyang I just noticed the comments there. Thanks for working on this issue. I think if we can't find the trading pair url, we can default it to the exchange url directly. maybe we can have that fill up and complete this tasks. Many thanks!!