Don't hide base class get_queryset.

And get the model object name from the model attribute that
get_object_dict expects to exist anyway. Reason:

class OscarListView(generic.ListView):
    def get_queryset(self):
        ...

class CustomListView(BulkEditMixin, OscarListView):
    # calling get_queryset on this class would resolve to BulkEditMixin.
    # get_queryset and return None.
Retrieve objects from get_queryset instead of default manager.

This allows a customized installation to prevent objects from being shown
(by ListView) and edited (by BulkEditMixin) in just one place,
get_queryset().