don't update last_pushed_timestamps until batch push completes
Fixes #37
Source isnt always credit card. Fixes #26
Name is optional as well.
make sure we serialize the id as well on the line_items since wombat requires at least an id on objects.
Add id for payment data
Fixes #41
Correct spec to use InventoryUnitSerializer like the ShipmentSerializer actually uses.
Dont set order#placed_on unless completed_at present & add Order totals & billing address to shipment.