Add support for choiceColumn in choice questions. Ref #378

[ruscoder]

I've added support for choiceColumn for choice questions. It's fully backward compatible because if no choiceColumn passed - the default getDisplay is used.

The usecase example:

  - text: Diagnoses
    type: choice
    linkId: diagnoses
    repeats: true
    answerValueSet: http://hl7.org/fhir/ValueSet/icd-10
    choiceColumn:
      - path: code
        forDisplay: true

[ir4y]

@ruscoder the same feature was implemented as part of https://github.com/beda-software/fhir-emr/pull/376/files#diff-606d3917dcaa9881fbf14f31e368ce6169f49d6c9b8bff6c3841798dc783ece3

It seems that that implementation is simpler than the one you provided.
Could you please review that implementation and provide your feedback.

[ruscoder]

It seems that that implementation is simpler than the one you provided. Could you please review that implementation and provide your feedback

I tried to solve it in a general way for not only Codings, but according to the specification, it does not make sense for non-Coding. Actually, your solution is good. Let's extract it from your PR as a separate PR that can be merged separately.