Build renderers into their individual npm packages (#7168)

This copies modules into three separate packages instead of
putting it all in React.

The overlap in shared and between renderers gets duplicated.

This allows the isomorphic package to stay minimal. It can also
be used as a direct dependency without much risk.

This also allow us to ship versions to each renderer independently
and we can ship renderers without updating the main react package
dependency.

index.js

@@ -1,4 +1,3 @@
-
 'use strict';
 
-module.exports = require('react/lib/ReactTestRenderer');
+module.exports = require('./lib/ReactTestRenderer');