This is required for sites that allow ranges to be browsed.

This change includes a datamigration to slugify existing range names.

Fixes #906

Most mixins will override functions of base classes and hence belong
before them.

Fixes #818

Filenames can easily get longer than 100 characters, and that causes
Django to fail hard (I think with a DatabaseError), because it's
currently not validated (see Django #11027)

This fix increases the character limit to 255 chars. Going much higer
can cause trouble with MySQL.

Fixes #625. Thanks for reporting go to @soloweb.

null=True is only useful for a few edge cases where one wants to
separate between '' and None.  If null=True was found, it was removed.
If blank=True was not set already, it was set instead.  If default=None
was set, it was removed (defaulting to '').

I then grepped the source code for tests 'is None' and 'is not None',
and checked the instances where default=None was set.

Fixes #584

Replace the import-time nav set-up with a settings-based one.  This is
more flexible ultimately although it doesn't allow extensions to easily
add their node automatically.  However this is probably a good thing
overall as it isn't easy to remove nodes in the previous impl.

Fixes 426

* Relocate 'Create new range' button to save space
* Bring breadcrumbs in line with offers
* Couple of minor corrections

They need registering using oscar.apps.offer.custom.create_range which
will create the model instance with the correct proxy class path.

After that, they will be available to see in the dashboard (but not
editable) and can be used in offers.

Fixes #385

* replaces all occurences of ``datetime.now()`` with
    ``django.utils.timezone.now()`` which returns aware or naive
    datetimes based on ``USE_TZ``
* increases ``South`` version to 0.7.6 in dependencies to make
    aware datetimes work in migrations.
* Oscar's sandbox is now configured to use aware timezones by
    default

Also split them into unit and functional tests.

You can now jump straight to editing products when creating a range.

Features:
* Basic crud
* Stats view