More PEP8 cleanup.
Use clean() instead of save() for setting ordering

This fixes a bug with django-mptt where it 
expects the ordering to be set when save() is
called.

Reference:
https://docs.djangoproject.com/en/dev/ref/models/instances/#django.db.models.Model.clean
Whitespace cleanup, clean() before save in tests
Remove distribute/setuptools breakage.
PEP8 and log statement cleanup.
Merge remote-tracking branch 'origin/sport81' into cosmania

Conflicts:
	shopkit/core/models.py
General cleanup.
Remove further references to customer.

* CustomerPaymentBase ABC.
* Allow customer fields to be blank.
* Unicode() without customer on order.
Removed no longer applicable help text.
Allow null for customer address as well.
Fixups to setup.
Define documentation build requirements.
Fixup Django settings for documentation build.
Updated reference to docs.
Added sorl optional dependency for docs.
Be more specific about requirements/dependencies.
Small fixup in category settings.
Backported working listener code.
Somehow, Sphinx doesn't like `in_shop` docstrings.
Remove wildcard import of listeners.