feature: mailing list

app/vkk/locale/de/LC_MESSAGES/django.mo

app/vkk/locale/de/LC_MESSAGES/django.po

...mplates/vkk/workhours/accounting/mailing_list/failed.html

...templates/vkk/workhours/accounting/mailing_list/form.html

...plates/vkk/workhours/accounting/mailing_list/success.html

app/vkk/templates/vkk/workhours/accounting/overview.html

app/vkk/workhours/accounting/mailing_list/__init__.py

app/vkk/workhours/accounting/mailing_list/forms.py

app/vkk/workhours/accounting/mailing_list/urls.py

app/vkk/workhours/accounting/mailing_list/views.py

app/vkk/workhours/accounting/urls.py