Add new form editor hello world

[SHOP-2450]

assets/js/src/form_editor/index.jsx

@@ -0,0 +1,14 @@
+import React from 'react';
+import ReactDOM from 'react-dom';
+
+const appElement = document.querySelector('#mailpoet_form_edit');
+
+if (appElement) {
+  ReactDOM.render(
+    <h1>
+      Here comes editor for:
+      {window.mailpoet_form_data.name}
+    </h1>,
+    appElement
+  );
+}