set up demo, exercise, final folders

step1-05/final/src/TodoApp.tsx

@@ -0,0 +1,16 @@
+import React from 'react';
+import { TodoFooter } from './components/TodoFooter';
+import { TodoHeader } from './components/TodoHeader';
+import { TodoList } from './components/TodoList';
+
+export class TodoApp extends React.Component {
+  render() {
+    return (
+      <div>
+        <TodoHeader />
+        <TodoList />
+        <TodoFooter />
+      </div>
+    );
+  }
+}