installation-cd-graphical: Enable the 'synaptics' touchpad driver

This is needed to get touchpad working in the installer on several
laptops. Tested on a Thinkpad X250.

Changed files
+1
nixos
modules
profiles
+1
nixos/modules/profiles/graphical.nix
···
enable = true;
displayManager.kdm.enable = true;
desktopManager.kde4.enable = true;
+
synaptics.enable = true; # for touchpad support on many laptops
};
environment.systemPackages = [ pkgs.glxinfo ];