the derivations build successfully again (except for the
universially-broken maps package), but were not yet proven to work with
the nixos module, since a configuration variable for the frontend
package was changed in this update.

wapkgs.nix new contains packages for several different versions of
workadventure (so far hasi + thecodingmachine), which can both be used.
Unfortunately, this appears to require some weird hacks to convince nix
to sort out the dependencies without having to actually duplicate all
the packaging code, but it works.

Maximal sharing means that even if the workadventure sources are imported
in all nix files, there will still only be one copy of it in the nix store
--- nevertheless, it seems reasonable to only have them once in the code,
too, if only to make upgrading them easier.

Builds fine, let's see if anything else works!