Nixos adapters

[MagicRB]

In it's current state, it works, but ideally it wouldn't enabled unless you want it, not sure how to achieve that.

[MagicRB]

I requested a review from you @pizzapim, the idea is there and solid. It still obviously needs work but I want to get this in so it's not sitting in a branch forever. Please take a look and let me know if you see anything. It has to be enabled through two hoops, first the undocumented argument __enableExperimentalNixOSCompatibility to makeSystem has to be set to true to even load the modules and then a surprise assertion has to be passed.

[pizzapim]

One thing I'm a bit worried about, is that NixNG modules' structures would have to be changed in order to fit into the NixOS model. But other than that, it's interesting. I do wonder expecially whether the automatic translation from systemd to init.services could ever exit the experimental stage though. Like you indicate, that could be a big source of bugs/security issues.