WIP: Repo of Markets/Exchanges

[uaktags]

Much to the same extent as iquidus#287, this is a pinned announcement of a collection of Exchanges. I don't want to be doing any more pull requests for exchanges as they seem to come and go all the time over the past 2-3years. Instead, I'll do PR's for them at this external repo and people can pick and choose what they want.

https://github.com/uaktags/iquidus-explorer-exchanges