Auto-populate debug select dropdowns from config.js THEMES

config.js

@@ -9,4 +9,13 @@ window.CONFIG = {
     theme: 'ash',
     units: 'metric',
     language: 'de'
+};
+
+// List of available themes. The key is the theme id (used in config.theme),
+// the value is the CSS file name. Add a new theme by adding a new entry here
+// and dropping the corresponding CSS file in the same directory.
+window.THEMES = {
+    'ash': 'ash.css',
+    'gruvbox': 'gruvbox.css',
+    'nord': 'nord.css'
 };