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/amd/_has.js

@@ -0,0 +1,10 @@
+define(['./_setup'], function (_setup) {
+
+  // Internal function to check whether `key` is an own property name of `obj`.
+  function has(obj, key) {
+    return obj != null && _setup.hasOwnProperty.call(obj, key);
+  }
+
+  return has;
+
+});