Some minor updates to the Binder docs and design fixes

[choldgraf]

This is a relatively minor PR to update some of the documentation configuration:

• It updates our noxfile.py to be a bit simpler and re-use the same environment
• It updates our conf.py to use the latest pydata theme configuration
• It updates our supporters and team code to generate better dark-friendly themes
• It adds a link to our discourse and updates the social links to be manually specified, which is what our theme recommends

[choldgraf]

Maybe @consideRatio would be willing to give a quick review since he is thinking about docs across the ecosystem as well?

[consideRatio]

This is a big big big big big deal for me. I've always felt confused about this repo. I'd love to see it renamed to something like this as well.

[consideRatio]

Opened #272