Change from django-tagging to django-taggit

Code changes required to render django-taggit tags instead of django-tagging tags,
also includes a management command to migrate django-tagging tags to django-taggit copied from https://github.com/kaleissin/django-taggit/commit/e3fe6f79bad444c4ad06bc530e80b3dab389131b

bin/django migrate_tagging_to_taggit

requirements
django-taggit==0.10.0
django-taggit-templatetags==0.4.6dev
django==1.4.6 (a requirement of django-taggit http://django-taggit.readthedocs.org/en/latest/)