Backoffice Formulare mit mehr Hinweisen versehen

src/backoffice/forms/assemblies.py

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

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

src/backoffice/templates/backoffice/assembly_auth.html

src/backoffice/templates/backoffice/assembly_members.html

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

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