Finish modularising config

There are still some things I want to change, but at least there aren't two systems now.

modules/eid.nix

@@ -8,6 +8,11 @@
 
   config = lib.mkIf config.chvp.eid.enable {
     environment.systemPackages = [ pkgs.eid-mw ];
+    nixpkgs.overlays = [
+      (self: super: {
+        firefox = super.firefox.override { pkcs11Modules = [ self.eid-mw ]; };
+      })
+    ];
     services.pcscd = {
       enable = true;
       plugins = [ pkgs.ccid ];