Extract method that applies the dashboard product list search query
Filter out products the the user isn't allowed to edit in one place

for all affected views. Also make it easy to customize or replace how
products are filtered for non-staff users.
Extract ordering the queryset into a method
Remove now unused method Product.is_user_a_partner_user
Merge pull request #1059 from mbertheau/partner-user-customizing

Partner user customizing

Conflicts:
	oscar/apps/catalogue/abstract_models.py