Allow source/collection admins to control visibility of repo versions separate from tags

[paynejd]

Right now, the visibility of a source/collection version is tied somewhat to its released and retired flags. This is especially true when using the latest keyword (which evaluates to "latest released version") or when evaluating a version-less reference, like /orgs/CIEL/sources/CIEL/concepts/1234/. We want administrators to have complete control over how OCL resolves these pointers, which means letting them set repo version visibility / behavior separately from flags.

In addition, we want to support the rest of the "flags" supported by the FHIR status field for CodeSystem, ValueSet, ConceptMap (draft | active | retired | unknown). Here's the publication status ValueSet: https://www.hl7.org/fhir/valueset-publication-status.html