refactor and modularize base.nix futher; use default.nix when possible

configuration/base/networking.nix

@@ -0,0 +1,26 @@
+{ pkgs, ... }:
+
+{
+  # networking.hostName = "nixos"; # Define your hostname.
+  # Pick only one of the below networking options.
+  # networking.wireless.enable = true;  # Enables wireless support via wpa_supplicant.
+  networking.networkmanager = {
+    # Easiest to use and most distros use this by default.
+    enable = true;
+    wifi.powersave = false;
+  };
+
+  # Configure network proxy if necessary
+  # networking.proxy.default = "http://user:password@proxy:port/";
+  # networking.proxy.noProxy = "127.0.0.1,localhost,internal.domain";
+
+  # Enable CUPS to print documents.
+  # services.printing.enable = true;
+
+  services.mullvad-vpn = {
+    enable = true;
+    package = pkgs.mullvad-vpn;
+  };
+
+  # services.resolved.enable = true;
+}