Login and error reporting on the encyclopedia gui

The old encyclopedia was allowing users to login. The only difference is that logged, users where getting a button where they can report a problem with a material and its representation (client/src/common/FlaggingFormPopup.js). This is not working anymore, since the old user management was discontinued.

We need to revive this feature based on the new user management. You find a simply how to for plain javascript here: https://www.keycloak.org/docs/latest/securing_apps/#_javascript_adapter

Ask Markus for the configuration details of our keycloak. Otherwise: https://repository.nomad-coe.eu/fairdi/keycloak (will change to somewhat nomad-lab.eu soon) realm: fairdi_nomad_prod, for test its fairdi_nomad_test (here localhost is allowed as redirect_url) client: nomad_public