Raise error in Fulfillment class if fulfillment processing fails
Add fulfilment behavior to Purchase and Order classes
Add quantity to shipments table
Add quantity validations to Shipment model
Rename Removable to Deletable
Add Activable interface spec
Add Committable interface spec
Add Deletable interface spec
Add Displayable interface spec
Add Fulfillable interface spec
Add Orderable interface spec
Use spec to enforce interface instead of abstract methods
Temporary disable unfulfill method spec; fix interface spec