added initial POC for flow support

Created by: torifat

POC for issue #324 (closed)

$ npm run create-react-app my-app
$ cd my-app
$ vim .flowconfig # copy template from: https://github.com/facebookincubator/create-react-app/blob/master/template/README.md#adding-flow
$ npm start

Instead of vim .flowconfig, you can do wget https://gist.githubusercontent.com/torifat/756443d1bab62abda5f87c3ca2c90dc8/raw/ab2464634e3b0cd873d0ff302a83a5097964276f/.flowconfig too.

Sample App.js:

/* @flow */
import React, { Component } from 'react';
import logo from './logo.svg';
import './App.css';

Math.pow('1212');

class App extends Component {
  render() {
    return (
      <div className="App">
        <div className="App-header">
          <img src={logo} className="App-logo" alt="logo" />
          <h2>Welcome to React</h2>
        </div>
        <p className="App-intro">
          To get started, edit <code>src/App.js</code> and save to reload.
        </p>
      </div>
    );
  }
}

export default App;

Sample Output: