gnome-control-center: meta fixes

Description was wrong, and add meta. Taken from Debian.
/cc maintainer @lethalman, also for the grandparent commit.

pkgs/desktops/gnome-3/3.16/core/gnome-control-center/default.nix

···
   '';
 
   meta = with stdenv.lib; {
-    description = "Single sign-on framework for GNOME";
+    description = "Utilities to configure the GNOME desktop";
+    license = licenses.gpl2Plus;
     maintainers = with maintainers; [ lethalman ];
     platforms = platforms.linux;
   };