Merge branch 'develop' into 'production'

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

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

src/backoffice/templates/backoffice/assembly_vouchers.html

src/backoffice/urls.py

src/backoffice/views/assemblies.py

src/backoffice/views/mixins.py

src/core/admin.py

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

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

src/core/management/commands/housekeeping.py

src/core/migrations/0093_vouchers.py

src/core/models/__init__.py

src/core/models/assemblies.py

src/core/models/conference.py

src/core/models/voucher.py

src/core/tests/vouchers.py