Merge react-scripts with upstream

[Oceanswave]

A few desirable changes have recently landed in upstream react-scripts -- Most notably the usage of webpack 3.x which brings some nice build speed improvements.

It would be great if these could land in create-react-app-typescript

[wmonk]

Yup there is an open PR for this at the moment. I am on holiday currently so won't be able to work on it until next week at the earliest.

[ianschmitz]

I believe webpack 3 still hasn't landed in an official release of react-scripts just yet. Looks to be slated for their 1.0.11 release.

facebook/create-react-app#2574