CUPS system wide client side remote printing.

Using lpr, lpq and so forth gets redirected to a remote printserver.

For those that might think that you cannot use NixOS as a print server, or use it in conjunction with a print server; you can already(in nixpkgs CUPS) relay print commands by editing your user ~/.cups/client.conf. This PR enables it for all local printing..

This has been tested and confirmed working. This change is also forwards and backwards compatible.