[USER STORY] Add an Order

[data-david]

As a: API user
I wish to: be able to import EU BIS e-Orders into the Reference Implementation
So that: It will end up as a Business transaction (similar to invoice)

Related to epic: #19

Link to design: N/A
Link to solution architecture:

Business value: (Critical/Important/Less important/Nice to have): Important

Link to example: https://github.com/difi/ehf-postaward-g3/blob/2019-05-30/structure/ordering-3.0/syntax/ehf-order-3.0.xml