Draft: Adding a GDPR banner

the code has been extended with a GDPR banner that explains the use of cookies and could also be used in this context to point out that this is a university project and not a productive site.

The base package is on npm @beyonk/gdpr-cookie-consent-banner and the customizations can be found at public/css/gdprbanner.css and public/js/gdprbanner.js.

The result is meant to be discussed together before it is merged into the master branch.