chore(controller): update djangorestframework to 2.4.4

See http://www.django-rest-framework.org/topics/release-notes#24x-series
and https://github.com/tomchristie/django-rest-framework/compare/2.4.3...2.4.4

Looks like bug fixes and one security fix in DRF 2.4.4, but I don't consider this essential for the 0.16 release.