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/allKeys.js

@@ -0,0 +1,13 @@
+import isObject from './isObject.js';
+import { hasEnumBug } from './_setup.js';
+import collectNonEnumProps from './_collectNonEnumProps.js';
+
+// Retrieve all the enumerable property names of an object.
+export default function allKeys(obj) {
+  if (!isObject(obj)) return [];
+  var keys = [];
+  for (var key in obj) keys.push(key);
+  // Ahem, IE < 9.
+  if (hasEnumBug) collectNonEnumProps(obj, keys);
+  return keys;
+}