This makes our build reproducible and consistent
* Disables dhall tests. They don't build in sandbox mode because they require network access
* Moves all scripts to ./scripts folder for consistency
* Moves all nix files to ./nix folder for consistency, except for release.nix which Hydra needs
* Changes convert.py to take the K8s swagger spec as an argument
* Get k8s swagger spec from nixpkgs
* Get dhall prelude from nixpkgs
* added an ./scripts/update-nixpkgs.sh script to easily update to a new version of nixpkgs
