Separate object_list counting step to method
Separate object_list counting step to method

This should help overrides for special cases, including external
caching needs.

pivotal-energy-solutions/django-datatable-view,pivotal-energy-solutions/django-datatable-view,doganmeh/django-datatable-view,pivotal-energy-solutions/django-datatable-view,doganmeh/django-datatable-view,doganmeh/django-datatable-view