Created by: bradfordlemley
This adds support for lerna and yarn workspace monorepos, https://github.com/facebookincubator/create-react-app/issues/1333.
There are some open questions as to how monorepos should work, so this is just a starting point.
Testing was performed with example and instructions at: https://github.com/bradfordlemley/cra-monorepo-examples
(Note: this PR pulls in changes from https://github.com/facebookincubator/create-react-app/pull/3435 which is for supporting running create-react-app in a monorepo space.)