Server-Side Rendering

In the initial page load, it would be great if React components be rendered to HTML server-side. Doing this would improve performance, compatibility, SEO, and reliability. We'd get these benefits without having to write our code once in PHP and then again in JavaScript.

I know this is a pretty major task, but there's some prior work that could serve as the foundation:
- The [v8js](http://php.net/manual/en/book.v8js.php) extension for PHP
- [ReactJS.net](http://reactjs.net/), which is React + ClearScript (the C# answer to v8js) + utility functions.
- [This server-side React with PHP tutorial](http://www.phpied.com/server-side-react-with-php/) from Stoyan Stefanov.

Start by reviewing the initial page-load path and the React/WP-API integration, then evaluate the referenced v8js, ReactJS.net, and PHP tutorial approaches. Done would mean React components are rendered to HTML server-side for the initial load while avoiding separate PHP and JavaScript implementations.

Written by the indexing model from the issue text.