📦 Created config files with common code

- Created common.nix for various configs
- Created theme.nix for theme related configs
- Moved some code to more logical files
- Moved some standalone files into nix multiline strings, in order to
  inject data

modules/networking.nix

@@ -1,9 +1,10 @@
-{ ... }:
-
+let
+  common = import ../common.nix;
+in
 {
   networking = {
     networkmanager.enable = true;
-    hostName = "nixos";
+    hostName = common.hostname;
     # wireless.enable = true;  # Enables wireless support via wpa_supplicant.
   };