Include studyGroup and componentResult attributes in the va-core model

[mbrush]

Following on the discussion in #250, I would like to include in the va-core model the sepio studyGroup attribute (on which the CAF cohort attribute is based), and similarly include the sepio componentResult attribute (on which the CAF subCohortFrequency attribute is based).

These were previously removed va-core, based on the argument that only one implementation uses them (CAF) - but I think one implementer is sufficient to warrant inclusion in the core model. And think it is helpful for incoming adopters to be able to see these attributes them there. They can remain 'draft' in va core until a second adopter implements, but I see no reason to not include them in the core model.