Motivation for this change

Currently, the package name of SLiM themes is just it's name. That leads to some problems:

• this name appears in installed packages (nix-env -q) and repolory
• it can get confused with other programs of the same name (e.g. https://repology.org/project/lunar/versions)
• it is not obvious that it is a theme
• naming is not consistent. other themes use the scheme numix-gtk-theme, adapta-kde-theme, deepin-sound-theme, see https://nixos.org/nixos/packages.html?channel=nixos-19.09&page=2&query=theme

So i propose to change the name to ${fullName}-slim-theme-${version}, e.g. nixos-slim-theme-testing.

I also changed the install directory name to just the fullName:

$ tree /nix/store/pfd6wi7n6l3k4r75a4i3dmr32dfqd8yv-nixos-slim-theme-testing
/nix/store/pfd6wi7n6l3k4r75a4i3dmr32dfqd8yv-nixos-slim-theme-testing
└── share
    └── slim
        └── themes
            └── nixos
                ├── background.png
                ├── LICENSE
                ├── panel.png
                ├── preview.png
                ├── README.md
                └── slim.theme

The Attribute name was not changed, so it should not break anything.

I don't use SLiM, so i would like to have at least one user test this change.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nix-review --run "nix-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

Notify maintainers

cc @jagajaga, @AndersonTorres