nixos: base

[despiegk]

• have vm support for nixos in grid
• allow one field which is full nixos configuration, so basically result is a full blown deployment
• create mdbook (docs) for the basics how to get started
• see how to cache the nixos build files (done by a user or by ourselves)

[xmonader]

story of nixos won't be continued, only micro/fullvm are implemented, but won't proceed any further