Yaml referencing other Yaml files

  * entityResolver.populateSpec is called for both catalog and yaml referencing items now to migrate attributes from the referee to the referred specs.
  * Reference catalog/YAML at any level
  * Catalog items referencing other catalog items (testParentCatalogDoesNotLeakBundlesToChildCatalogItems) should not make their bundles visible to the referenced catalog item.
  * Catalog items referencing external YAML (testCatalogLeaksBundlesToReferencedYaml) should make their bundles visible to the referenced yaml as discusses in the spring planning conference.

I will add comments as the method names to not describe the intent clearly.