Add new user to Role named 'user' on insert.

Also fix cascade relationships between User and UserRole.
update tests for auto-add of new user to Role 'user'
remove anonymous/authenticated roles frmo populate + add 'user'

We also change roles_id in PriceModifier to be nullable and fixup role
and product relations. Various fixtures and tests updated to match.
selling_price and tier_pricing changes for undef PriceModifier roles_id