Transitive dependencies

[charleso]

Currently the generated dependencies are not handled at all, and this will almost certainly result in broken builds. Nix doesn't really do transitive dependencies, except for propagatedBuildInputs. We might be able to use that (although it doesn't seem to be working for me at the moment) or alternatively generate the dependencies at every level.

We should try to respect the relevant confs, but that is probably going to get messy.