New port: www/py-django-common-helpers

py-django-common-helpers consists of the following things:

• Middleware that makes sure a web-app runs either on or without "www" in the domain.

• "SessionManagerBase" base class, that helps in keeping session related code object-oriented and clean.

• "EmailBackend" for authenticating users based on their email, apart from username.

• Custom db fields that can be used in models including a "UniqueHashField" and "RandomHashField".

• Bunch of helpful functions in helper.py

• "render_form_field" template tag that makes rendering form fields easy and DRY.

• Couple of dry response classes: "JsonResponse" and "XMLResponse" in the django_common.http that can be used in views that give json/xml responses.

WWW: https://github.com/tivix/django-common/

Approved by: miwi (mentor)
Differential Revision: https://reviews.freebsd.org/D19544