Adding changelog for django 1.7 support and dropping django 1.4 support.
Adding changelog for django 1.7 support and dropping django 1.4 support.

gradel/django-sortedm2m,gradel/django-sortedm2m,fabrique/django-sortedm2m,gregmuellegger/django-sortedm2m,fabrique/django-sortedm2m,fabrique/django-sortedm2m,gradel/django-sortedm2m,gregmuellegger/django-sortedm2m,gregmuellegger/django-sortedm2m