client_and_server.js and client_only.js not being loaded by latest webpacker

The installer assumes to put these files into the javascript/packs folder where they used to be picked up by Webpacker, but this is not the case anymore. 

Either we need to add React and ReactDOM import in application.js (which does work) or figure out what else has to be done to get Webpacker to recognise these files.