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/lastIndexOf.js

@@ -0,0 +1,9 @@
+define(['./_createIndexFinder', './findLastIndex'], function (_createIndexFinder, findLastIndex) {
+
+	// Return the position of the last occurrence of an item in an array,
+	// or -1 if the item is not included in the array.
+	var lastIndexOf = _createIndexFinder(-1, findLastIndex);
+
+	return lastIndexOf;
+
+});