Upgrade to webpack v2

Created by: Timer

webpack has had its first v2 release!

There are a few changes we're waiting on:

• babel-loader@6.2.10
• webpack-dev-server@2.2.0-rc.0
• https://github.com/ampedandwired/html-webpack-plugin/pull/526
• extract-text-webpack-plugin#309
• remove LoaderOptionsPlugin for prod postcss
  • https://github.com/webpack/extract-text-webpack-plugin/issues/265
  • https://github.com/webpack/extract-text-webpack-plugin/issues/281

would be nice:

• Check up on https://twitter.com/simplesthing/status/823674445843734528 – is this affecting us?
• https://github.com/webpack-contrib/extract-text-webpack-plugin/issues/294
• https://github.com/webpack-contrib/extract-text-webpack-plugin/issues/366

/cc #183 (closed)