Download groups in OH-queue-friendly format

[japplefield]

$ agio groups --list downloads in a format that looks like this:

[299866] achitta
[300195] chenmar, yuntongz
...

Very readable, but the OH queue expects a JSON that looks like this:

[["nuppula@umich.edu","sarangia@umich.edu","svejp@umich.edu"],
["bybwang@umich.edu","chungwil@umich.edu","marxd@umich.edu"],
["nksuram@umich.edu"]]

Add a setting that formats the group list like this for easy copy-pasting into the OH queue Bonus points: an extension that also makes a PUT to https://eecsoh.eecs.umich.edu/api/queues/<queue-id>/groups with groups directly from the Autograder. (OH Queue source code)