RMA Refactoring
API ReturnAuthorizationController fixes
RMA Spec Fixes
Fix Improper create statement in ReturnAuthorization, Specs
fix syntax error for checkout spec, mark pending specs which depend on shipping calculators
Fix remaining RMA specs in core, reduce amount of spec setup needed
fix checkout_controller_spec
fix request checkout spec
Add Stock::Quantifier and Stock::AvailabilityValidator to ensure sufficient stock is available to fulfill order
Adding test coverage for eed16c74
[core] various refactoring:

* Use ruby19 hash syntax
* Add lambda to scopes
[core] Refactor Spree::InventoryUnit:

* Use symbol for state machine consistency
* Re-enable commeted out test for #finalize_units!
* Use scope shipped in .backordered_for_stock_item
Refactor lambda to -> notation
Refactor Spree::Zone:

* ruby19 hash syntax
* indentation
* scope logic refactor
Fix ambiguous column name in UpdateShipmentStateForCanceledOrders
migration

[Closes #2792]
Revert "Fix ambiguous column name in UpdateShipmentStateForCanceledOrders"

This reverts commit 0c04aade284df9eb06adee5fb6fb3b9db5d4f43a.

rake test_app was getting SQLite3::SQLException: near ".": syntax error
Revert "Refactor lambda to -> notation"

This reverts commit 6cfd0144f466432f22675be16349d728bf993bb0.

Conflicts:
	core/app/models/spree/shipment.rb
	core/app/models/spree/zone.rb
Refactor Spree::Calculator and Spree::Classification
Updated rspec syntax and spree namespacing for readability.

Fixes #2777
Fix file mode bits taxonomies controller

Fixes #2800