bird-lg: remove Moved to dn42.nix along with other dn42 services.
matrix-appservice-irc: init at 0.22.0
bird-lg: init at 2020-05-20-unstable
Redefine package set on top of overlays I wanted to reduce duplication, but ended up somewhat in the same place (with manifest.nix). Yet I find it much more elegant.