Expand the context of use for the value set reference extension to support use on the Codeable Concept

Expand the context of use for the value set reference extension to support use on the Codeable Concept

The example is for QI-Core capability to reference a value set extension to indicate that a a code (I.e., the thing not done in this ProcedureNotDone profile) to reference a single code (one thing not done), more than one code (several things not done) and a uri (nothing in the the entire value set was done - I.e., "I didn't do any of these"). To allow more than one thing not done, the value set reference would need to be a Codeable Concept for the reference extensions. (see: http://hl7.org/fhir/us/qicore/StructureDefinition-qicore-procedurenotdone.html). There are 8 QI-Core "notDone" profiles that would benefit from this change

1. QICoreCommunicationNotDone
2. QICoreDeviceNotRequested
3. QICoreImmunizationNotDone
4. QICoreMedicationAdministrationNotDone
5. QICoreMedicationDispenseNotDone
6. QICoreMedicationNotRequested
7. QICoreObservationNotDone
8. QICoreProcedureNotDone
9. QICoreServiceNotRequested