Initial commit: Developer Tools MVP with visual editor

- Complete React app with 7 developer tools
- JSON Tool with visual structured editor
- Serialize Tool with visual structured editor
- URL, Base64, CSV/JSON, Beautifier, Diff tools
- Responsive navigation with dropdown menu
- Dark/light mode toggle
- Mobile-responsive design with sticky header
- All tools working with copy/paste functionality

node_modules/underscore/modules/pluck.js

@@ -0,0 +1,7 @@
+import map from './map.js';
+import property from './property.js';
+
+// Convenience version of a common use case of `_.map`: fetching a property.
+export default function pluck(obj, key) {
+  return map(obj, property(key));
+}