unix-tools: introduce unix-tools.nix

unix-tools.nix has a collection of tools that are commonly installed
by default in Unix derivatives. This is intended to provide
compatibility between macOS and Linux users. Three Linux-only
derivations are provided for compatbility:

- procps
- utillinux
- nettools

More tools are also provided.

Also: treewide: use unixtools

Non-comprehensive replace of Linux-only procps and util-linux with
'unixtools'.

pkgs/servers/xmpp/biboumi/default.nix

@@ -1,5 +1,5 @@
 { stdenv, fetchurl, fetchgit, cmake, libuuid, expat, sqlite, libidn,
-  libiconv, botan2, systemd, pkgconfig, udns, pandoc, procps } :
+  libiconv, botan2, systemd, pkgconfig, udns, pandoc, coreutils } :
 
 stdenv.mkDerivation rec {
   name = "biboumi-${version}";
@@ -20,12 +20,11 @@ stdenv.mkDerivation rec {
 
   nativeBuildInputs = [ cmake pkgconfig pandoc ];
   buildInputs = [ libuuid expat sqlite libiconv libidn botan2 systemd
-    udns procps ];
+    udns ];
 
-  inherit procps;
   preConfigure = ''
     substituteInPlace CMakeLists.txt --replace /etc/biboumi $out/etc/biboumi
-    substituteInPlace unit/biboumi.service.cmake --replace /bin/kill $procps/bin/kill
+    substituteInPlace unit/biboumi.service.cmake --replace /bin/kill ${coreutils}/bin/kill
     cp $louiz_catch/single_include/catch.hpp tests/
     # echo "policy_directory=$out/etc/biboumi" >> conf/biboumi.cfg
     # TODO include conf/biboumi.cfg as example somewhere