Merge branch 'feature/backoffice_users' into 'develop'

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

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

src/backoffice/templates/backoffice/user-block.html

src/backoffice/templates/backoffice/user-detail.html

src/backoffice/templates/backoffice/user-list.html

src/backoffice/templates/backoffice/user-rename.html

src/backoffice/urls.py

src/backoffice/views/mixins.py

src/backoffice/views/users.py

src/core/migrations/0055_backoffice_users_perms.py

src/core/models/conference.py