Add ui subfolder, bootstrapped a "hello-world" React-Admin app, changed Makefile to start both apps in dev mode

ui/src/index.js

@@ -0,0 +1,12 @@
+import React from 'react'
+import ReactDOM from 'react-dom'
+import './index.css'
+import App from './App'
+import * as serviceWorker from './serviceWorker'
+
+ReactDOM.render(<App />, document.getElementById('root'))
+
+// If you want your app to work offline and load faster, you can change
+// unregister() to register() below. Note this comes with some pitfalls.
+// Learn more about service workers: https://bit.ly/CRA-PWA
+serviceWorker.unregister()