backoffice/assemblyteam: room positioning view

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

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

...ce/templates/backoffice/assemblyteam_assembly_detail.html

.../templates/backoffice/assemblyteam_editposition_room.html

src/backoffice/urls.py

src/backoffice/views/assemblyteam.py

src/core/models/rooms.py