📦 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

common.nix

@@ -0,0 +1,23 @@
+rec {
+  keymaps = {
+    layout = "gb,no";
+    options = "grp:alt_shift_toggle"; # Toggle using ALT + SHIFT
+  };
+
+  username = "martin";
+  hostname = "nixos";
+
+  dir = {
+    home = "/home/${username}";
+    pictures = "${dir.home}/Pictures";
+  };
+
+  # This value determines the NixOS release from which the default
+  # settings for stateful data, like file locations and database versions
+  # on your system were taken. It‘s perfectly fine and recommended to leave
+  # this value at the release version of the first install of this system.
+  # Before changing this value read the documentation for this option
+  # (e.g. man configuration.nix or on https://nixos.org/nixos/options.html).
+  system.version = "24.11";
+  terminal = "kitty";
+}