Some description fixes

There are many more packages to fix, this is just a start.

Rules:
 * Don't repeat the package name (not always that easy...)
 * Start with capital letter
 * Don't end with full stop
 * Don't start with "The ..." or "A ..."

I've also added descriptions to some packages and rewritten others.

pkgs/tools/graphics/argyllcms/default.nix

@@ -77,7 +77,7 @@ stdenv.mkDerivation rec {
 
   meta = with stdenv.lib; {
     homepage = http://www.argyllcms.com;
-    description = "An ICC compatible color management system";
+    description = "Color management system (compatible with ICC)";
     license = licenses.gpl3;
     maintainers = [ maintainers.rickynils ];
     platforms = platforms.linux;