Merge branch 'feature/public_room_flag' into 'develop'

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/plainui/tests.py

src/plainui/views.py