Require Django at least Django 1.8
Require Django at least Django 1.8

This branch contains some changes that simply won't work with <1.8 anymore.

jnns/django-import-export,django-import-export/django-import-export,daniell/django-import-export,bmihelac/django-import-export,bmihelac/django-import-export,jnns/django-import-export,bmihelac/django-import-export,django-import-export/django-import-export,django-import-export/django-import-export,django-import-export/django-import-export,jnns/django-import-export,daniell/django-import-export,jnns/django-import-export,bmihelac/django-import-export,daniell/django-import-export,daniell/django-import-export