nixui issues

Update to newer nwjs

As mentioned in https://github.com/NixOS/nixpkgs/pull/27882, we can’t really throw out the old, unmaintained versions of nwjs until `nixui` supports them.

Profpatsch

assumes /etc/nixos/hardware-configuration.nix?

I don't have this file but see this message on launch: ``` [11731:0313/124603:INFO:CONSOLE(839)] "Uncaught Error: ENOENT: no such file or directory, stat '/etc/nixos/hardware-configuration.nix'", source: fs.js (839) ```

dtzWill

Work-around for npm's hardlinks handling.

I couldn't run nixui on my system because of autooptimization problems (see https://github.com/NixOS/npm2nix/issues/26). This works around those by making a copy of sources.

ktosiek