Add basic "order interfacing" service and reorg existing classes
This commit adds a very basic service for "interfacing" orders which is
the CBS terminology for commiting and finalizing an order. It also
reorganizes the namespaces for the existing Order
classes to support
the upcoming API restructure.
API breaking change, bumped to new major version (4.0.0).
Please review: @ahoffmann @weizhong-wang @lloyd-carter