- Set Meta.app_label on models created in the tests
- Use logging.NullHandler instead of django.utils.log.NullHandler
- Use oscar.core.loading.get_model() instead of django's get_model
- Remove template tags '{% load url from future %}'
Allow custom benefits to be registered and used in offers
This alters the benefit model to allow proxy class to be registered.
The dashboard flow is tweaked to allow such classes to be selected once
they've been registered.
A dummy custom benefit is included in the sandbox.