Add teams list view

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

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

src/backoffice/templates/backoffice/teams/list.html

src/backoffice/tests/__init__.py

src/backoffice/tests/teams/__init__.py

src/backoffice/tests/teams/teams.py

src/backoffice/urls.py

src/backoffice/views/teams/__init__.py

src/backoffice/views/teams/teams.py