Upgrade Django to 1.9

[berkerpeksag]

TODOs

• Use builtin LoginRequiredMixin: https://docs.djangoproject.com/en/1.9/releases/1.9/#permission-mixins-for-class-based-views
• Upgrade django-pipeline to 1.6.x+ to support Django 1.9
• Upgrade django-* packages to support Django 1.9
• Read Django 1.9 release notes: https://docs.djangoproject.com/en/1.9/releases/1.9/
• https://docs.djangoproject.com/en/1.9/ref/django-admin/#cmdoption-test-parallel
• Use builtin JSONField
• Check that we have PostgreSQL 9.4 on servers