wip: create SalesOrder classes and specs
Allow adding items following same pattern as Invoice
Model SalesOrderItem & List the same wasy as InvoiceItem & List
Add the order_status field (set to _pendingFulfillment, for example)
Added #get shortcut.

Infers internal ID hash when a non-Hash is passed to #get
Assign internal ID when record creation is successful
Merge branch 'sales-order-fix' into sales-order
Fix regression to update action- should return boolean true if success