nordic: add the Nordic-Polar themes
nordic: add the Nordic-Polar themes

Nordic-Polar is the light version of the Nordic themes. Although the
author keeps it in a separate git repository, they are organized in
the very same way. They are also distributed together in
https://www.pling.com/p/1267246/, the primary site used by the author
for distribution.

Adding Nordic-Polar to the nordic package makes maintainance easier.

NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs