License code under AGPL-3.0-or-later, and everything else under
CC-BY-SA-4.0. This is pretty much what we arrived at in the discussion
in #109 which has been open since two years, and in a recent team
discussion following up on that. Even though we couldn't reach everyone
we believe this is in spirit of the project, and if anybody who
contributed code or anything else in this repository is not fine with
this license change, let me know and I'll be happy to replace the
content or rewrite the code.

Bump year to 2022 in copyright notices while at it.

Close: #109