* Add `PUBLIC_URL` env variable for advanced use (#937)
* Add support for `PUBLIC_URL` env variable
* Remove unnecessary duplications
* Simplify served path choice logic
* Honor PUBLIC_URL in development
* Add e2e tests

Enables serving static assets from specified host.

- code style

* E2E: run tests when react is ready

* Entangle e2e with callbacks

* Remove unused e2e lines

* Use a more sophisticated template for end-to-end testing.

* Not publish integration tests to npm

* Use "commander" for  cli argv handling

* Handle different scripts version forms and exits without a name given

* Prepare the commands for testing with a template

* Fix dev "template" path

* Add various features to test

* Test various features separately

* Test language features

* Comment unused e2e.sh lines

* Add "development" tests

* Test environment variables

* Test webpack plugins

* Replace kitchensink README

* Switch integration tests from jest to mocha

* Use `fs-extra`

* Use the correct folders

* Do some cleanup

* Print a better message for `--template`

* Test `npm start` with and without https

* Separate fast e2e testing from kitchensink testing

* Hide `--internal-testing-template` (former `--template`) CLI option