Allow disabling of console clearing

Created by: hyperknot

When debugging an ejected script via console.logging different things, I found it quite difficult / annoying that multiple pieces of this script clear the the console when it detects stdout.isTTY (start.js and react-dev-utils/WebpackDevServerUtils.js).

I would like to recommend some kind of argument or environment variable to disable that behaviour, so that we wouldn't need to eject and modify and clone to simply enable console logging.