A directory-category for terminal emulators

This is a mostly cosmetical commit, in the sense it doesn't change the contents
of any package, but reorganizes the overall Nixpkgs expressions.

Terminal emulators are an ubiquitous tool for any Unix user; even the beginners
are routinely familiarized to it. And, manifestly, there are many
implementations of terminal emulators out there, from those traditionally made
in C and C++ to those written in Haskell and Go.

Terminal emulators deserve more highlight. This commit does that by creating a
category for them.

pkgs/applications/terminal-emulators/termite/wrapper.nix

@@ -0,0 +1,15 @@
+{  makeWrapper, symlinkJoin, configFile ? null, termite }:
+
+if configFile == null then termite else symlinkJoin {
+  name = "termite-with-config-${termite.version}";
+
+  paths = [ termite ];
+  nativeBuildInputs = [ makeWrapper ];
+
+  postBuild = ''
+    wrapProgram $out/bin/termite \
+      --add-flags "--config ${configFile}"
+  '';
+
+  passthru.terminfo = termite.terminfo;
+}