Add deprecation notice for Variant#in_stock?'s quantity argument

Advise people to use can_stock? instead
Clear changelogs
Add changelog entry for Variant#in_stock quantity parameter deprecation
Simplify Variant#can_stock? test

This functionality is already tested within the Quantifier class

Conflicts:
	core/spec/models/spree/variant_spec.rb
Payments with AVS response codes of 'M' are not to be considered risky

Fixes #4251
remove the guard, not needed anymore

fixes #3985
fixes #4246
Add changelog for #4251
Iterate through groups of inventory units rather than each inventory unit one at a time in Shipment#to_package

Imagine in the case where there are 100 inventory units for the shipment. In this situation, the old code was calling this code 100 times:

package.add inventory_unit.line_item, 1, inventory_unit.state_name

Conflicts:
	core/app/models/spree/shipment.rb