refactoring of ParentMixin: - add more queryset filters - rename lookup method - add cache parameter to prefetch method
refactoring of ParentMixin:
- add more queryset filters
- rename lookup method
- add cache parameter to prefetch method

ulule/pybbm,ulule/pybbm,thoas/pybbm,ulule/pybbm,thoas/pybbm,thoas/pybbm