use same script to interrogate tracking_list, then get the object targeted by script
Owner, Site, Resource, or VariationCategories

This will improve consistency in UI because at_date parameter is handled in same way
for all of displayed properties.

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@42630 20353a03-c40f-0410-a6d1-a30d3c3de9de