- Update webpack-contrib to next
- Replace ExtractTextPlugin with MiniCssExtractPlugin, but pin to 0.4.2
  until shellscape/webpack-manifest-plugin#167 is resolved.
- Replace removed CommonsChunkPlugin with `optimize.splitChunks`
  configuration option
- Remove plugins provided by `mode` configuration option:
  NamedChunksPlugin, NamedModulesPlugin, and DefinePlugin
- Use terser-webpack-plugin over uglifyjs-webpack-plugin-terser
- Upgrade to webpack-mild-compile@3.3.1
- Force CSS splitting by entry
- Filter css order warnings
- Add optimize-css-assets-webpack-plugin to dist config
- Update tapable typings