Add a group in mass mailing to focus only on reviewer without profile, closes #187

src/strass/strass_app/forms.py

src/strass/strass_app/locale/en/LC_MESSAGES/django.po

src/strass/strass_app/locale/fr/LC_MESSAGES/django.po

src/strass/strass_app/tests/test_mass_mailing.py