Align with FHIR Sequence resource where possible

[buske]

Here's the current version from FHIR: https://www.hl7.org/fhir/2016Jan/sequence.html#resource

[Relequestual]

There at least half a dozen initatives like this. We're part of the Global Alliance. This issues seems at odds with the GA initative of interoperability in this sense. Kind of competing standards.