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/workbox-window/utils/WorkboxEvent.js

@@ -0,0 +1,20 @@
+/*
+  Copyright 2019 Google LLC
+
+  Use of this source code is governed by an MIT-style
+  license that can be found in the LICENSE file or at
+  https://opensource.org/licenses/MIT.
+*/
+import '../_version.js';
+/**
+ * A minimal `Event` subclass shim.
+ * This doesn't *actually* subclass `Event` because not all browsers support
+ * constructable `EventTarget`, and using a real `Event` will error.
+ * @private
+ */
+export class WorkboxEvent {
+    constructor(type, props) {
+        this.type = type;
+        Object.assign(this, props);
+    }
+}