Merge branch 'develop' into feature/#66-fehlerseiten

src/api/tests/workadventure.py

src/api/views/conferencemember.py

src/backoffice/locale/de/LC_MESSAGES/django.po

src/backoffice/locale/en/LC_MESSAGES/django.po

src/backoffice/templates/backoffice/login.html

src/core/admin.py

src/core/locale/de/LC_MESSAGES/django.po

src/core/locale/en/LC_MESSAGES/django.po

src/core/migrations/0050_Room_is_public_fahrplan.py

src/core/models/rooms.py

src/core/models/users.py

src/core/sso.py

src/plainui/jinja2/plainui/base.html

src/plainui/jinja2/plainui/components/calendar.html

src/plainui/jinja2/plainui/components/livestream.html

src/plainui/jinja2/plainui/landing.html

src/plainui/jinja2/plainui/public_fahrplan.html

src/plainui/static/plainui/img/rc3-landing-videoposter.jpg

src/plainui/static/plainui/js/modal.js

src/plainui/styles/_button-classes.scss