Renaming the edit_line_items method to cart. Also since they were on the same line, assigning a proper icon for the cart page
In checkout.rb we first create_proposed_shipments but here we check if addresses are valid. If not we need to destroy_all instead of delete_all so that the inventory_units that were created by create_propsed_shipments will also be destroyed and not clutter up the DB
Eliminate unnecessary instance var