global rename of 'Venue' to 'Assembly'

src/api/serializers.py

src/api/urls.py

src/api/views/assemblies.py

src/api/views/mixins.py

src/api/views/rooms.py

src/api/views/users.py

src/backoffice/forms.py

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

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

src/backoffice/templates/backoffice/assembly_create.html

src/backoffice/templates/backoffice/assembly_detail.html

src/backoffice/templates/backoffice/assembly_edit.html

...ackoffice/templates/backoffice/assembly_editchildren.html

src/backoffice/templates/backoffice/assembly_editlinks.html

src/backoffice/templates/backoffice/assembly_list.html

src/backoffice/templates/backoffice/base.html

src/backoffice/templates/backoffice/index.html

src/backoffice/templates/backoffice/staticpage_detail.html

src/backoffice/templates/backoffice/staticpage_form.html

src/backoffice/templatetags/c3assemblies.py