update webpack, update packages, dev experience

update webpack, clasp, client code, eslint, prettier, readme, packages to latest

src/client/MainDialog.jsx

@@ -0,0 +1,7 @@
+import React from 'react';
+import ReactDOM from 'react-dom';
+import SheetEditor from './components/SheetEditor';
+
+import './styles.css';
+
+ReactDOM.render(<SheetEditor />, document.getElementById('index'));