Create #explorer infrastructure

[cbeams]

• Create Slack channel (#explorer)
• Fork grazcoin/bisq-explorer repo and republish as bisq-network/explorer
• Set up notifications from GitHub repo => Slack channel
• Register repo in .mrconfig / .gitignore
• Link repo to #dao ZenHub board
• Create bisq-network/roles issue as appropriate (BSQ Explorer Operator roles#11)
• Update bisq-network/roles README as appropriate
• Create GitHub team as neccessary
• Grant GH team admin rights to repo

[cbeams]

Closing as complete, but note that the explorer app itself is still being run by @grazcoin, and therefore cannot be updated until we've migrated that to a new operator. This work will be managed as issues in the bisq-network/explorer repository.

[cbeams]

(And of course, @grazcoin, you're welcome to continue maintaining and operating the explorer if you like! We'll just need to discuss what that's going to look like from here out.)