Allow custom score server domains

New

• If you want to serve Aferlight Caves from a different domain from the score server you can set the SCORE_SERVER_SCHEME and SCORE_SERVER_DOMAIN variables in build-prod.sh. Then, when you build a production version with npm run build requests for scores will be sent to the custom score server domain. By default score requests are still sent to the same domain the static content is being served from.
• Added a clean npm script that removes the results of the build script.

Fixed

• Updated the @babel/cli dev dependency to resolve some minor security vulnerabilities.