Create FHIR server registry resource provider and related persistence interceptor

[JohnTimm]

Issue #832 makes the FHIR registry more dynamic adding the ability for individual FHIR registry resource providers to manage the resources that are contributing to the registry and enabling the possibility that the resources are provided by a FHIR server. This story covers the creation of a FHIR server registry resource provider that asks the FHIR persistence layer for resources by URL and version and optionally caches them in memory. This story might also include a persistence interceptor that can be used to invalidate the cache when new versions of the resources come into the FHIR server.