tidy up spree preferences testing support
[api] Added a CheckoutsController
- Allows creation of a new, empty order
- Can transition an order from cart to complete state
- Removed now unneeded address and delivery actions from API's
  OrdersController
[api] Added support for updating an order's payments using CheckoutsController
move rabl configure into after_initilize block to fix rails generator
error
Added Users controller to API
WIP Ability changes to allow record level permissions
Add instance level permissions in Admin controller  /
ResourceController, and encourage more use for CanCan's
accessible_by method. Re-adds ability specs that were in
spree_auth_devise
Drop debugger
Drop admin user controller