Initial concept of list properties
Add framework for pluggable applications
Add database migration for custom list properties
Fixup initial creation of properties forms for lists
Fixup variables for custom list properties
Slight optimization for variable replacement
Change to official patch for 1.8.2
Fix clobber of property and list item sorting
List items can be disabled
Merge pull request #738 from greezybacon/feature/equipment

Reviewed-By: Peter Rotich <peter@osticket.com>