Handle shipping method filtering in Spree::Stock::Estimator
Add stock location to shipments
Remove deprecated Spree::InventoryUnit.backorder scope
Add method to retrieve a list of backordered inventory units for a particular stock item
Move responsibility of processing backorders from Spree::Variant to Spree::StockItem

This will also only process backorders which are relevant for this stock item's stock location
create shipping calculators to work with content_item arrays
Remove product on_hand methods
Remove references to count_on_hand and on_hand methods for Products and Variants
Remove count_on_hand tests from variant
WIP Remove #rate_hash from order
Remove #rate_hash from order
make inventory units pending while they are in the cart, set pending to false on order checkout
Remove show_zero_stock_products preferences
Remove mentions of variant#in_stock?
seed stock locations and create stock items for variants
Remove on_demand from both variants and products
Order#finalize! now deals with stock items count_on_hand
Migration to remove on_demand from products and variants
Added increase_stock_for_variant to StockLocation
Get InventoryUnit to work with shipments and stock items