Since there is no demo or us site anymore we can simplify the structure
somewhat by moving the sandbox one directory up

We only support two versions of Django. That policy might change given
that Django has started doing LTS releases. But for now, it only makes
sense to remove Django 1.7 support.

This commit adds the python_2_unicode_compatible decorator to all models
that define a text representation. Furthermore, it adds a test to ensure
that we never forget to do that.

It is explained in details in the Django docs:
https://docs.djangoproject.com/en/dev/topics/python3/#str-and-unicode-methods

This is to keep the sandbox as vanilla as possible, as it's the
environment that migrations should be built against.

Wrap the custom user classes in a conditional block.

This can be used by new Oscar installs.  It's the same as a the core
Django one but without a username.

The new model must have an email field but Oscar will work without
anything else.

These are simpler as they are guaranteed to have an email field which
Oscar uses for authentication.

* Emailbackend: Updated to use REQUIRED_FIELDS
* Demo and sandbox site now use compat.AUTH_USER_MODEL as well
* Added example custom user that gets tested for Django >= 1.5

Example sites now sit in their own folder (sites) for easier
organisation.

It handles the situation where there is no profile model too, and
dyncamically builds a profile and user form