Merge branch 'master' into issue65

apps/official/BiscuIT-App-Alsijil

apps/official/BiscuIT-App-Chronos

apps/official/BiscuIT-App-Exlibris

apps/official/BiscuIT-App-SchILD-NRW

apps/official/BiscuIT-App-Untis

biscuit/core/forms.py

biscuit/core/locale/ar/LC_MESSAGES/django.po

biscuit/core/locale/de_DE/LC_MESSAGES/django.po

biscuit/core/locale/fr/LC_MESSAGES/django.po

biscuit/core/locale/nb_NO/LC_MESSAGES/django.po

biscuit/core/locale/tr_TR/LC_MESSAGES/django.po

biscuit/core/menus.py

biscuit/core/migrations/0016_parent_groups.py

biscuit/core/migrations/0017_group_name_length.py

biscuit/core/models.py

biscuit/core/settings.py

biscuit/core/static/img/biscuit-logo.png

biscuit/core/static/img/biscuit-logo.svg

biscuit/core/templates/core/base.html

biscuit/core/templates/core/error.html