[backend] Persist 'only show completed orders' checkbox across pagination requests

Fixes #4004
Add changelog entry for #4004
When removing defunct zone members use classify instead of capitalize when deleting zone members by zonable_type.

When creating a custom zone member type like zip_code for example using capitalize removes all models with zonable type != Spree::Zip_code instead of Spree::ZipCode

Fixes #4001
Inventory Tracking by Variant: fix resource controller model load issue

Fixes #4016