auto/manual init w/ single bundle, BYO root element 🎉 (#1173)

* ensure that application is only initialized once

* allow for single bundle init

* enable manual initialization via global flag

webpack.dev.js

@@ -13,7 +13,6 @@ module.exports = merge.smart(require('./webpack.base.js'), {
       `webpack-dev-server/client?http://${ HOST }:${ PORT }/`,
       './index',
     ],
-    init: './init',
   },
   output: {
     path: path.join(__dirname, 'dist'),