quickgui: add quickemu to PATH

[heyimnova]

Description of changes

Add quickemu to PATH for quickgui so the user does not need to install it separately to use quickgui. Also add license for quickgui, correct meta.platforms, add zenity so the file picker works, and make some other general improvements to the package.

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandboxing enabled in nix.conf? (See Nix manual)
  • sandbox = relaxed
  • sandbox = true
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 23.11 Release Notes (or backporting 23.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

[flexiondotorg]

I lead the upstream Quickemu project. I have tested these changes locally, and it is an improvement to the user experience as Quickgui works as expected "out of the box" without additional knowledge of having to install quickemu.

[Aleksanaa]

@ofborg build quickgui

[github-actions]

Successfully created backport PR for release-23.11:

• [Backport release-23.11] quickgui: add quickemu to PATH #308364