Allow REQUIRE_MAIL_DOMAIN to not exist in addition to it being empty
Undo changes in config/locales/de_DE.yml
changed .env variable name to GREENLIGHT_ACCOUNT_HD; allowed only comma and no whitespace as separator
Allow the admin to change email-addresses, just enforce domain on registration
Co-authored-by: Gaja Sophie Peters <gaja.peters@uni-hamburg.de>
Co-authored-by: Ahmad Farhat <ahmad.af.farhat@gmail.com>