Warn about unused resources

[ielis]

The validator should point out presence of unused MetaData > Resources, that is resources that do not correspond to any OntologyClass.

@julesjacobsen @pnrobinson the Phenopacket Schema documentation requires presence of resources for used OntologyClasses, but does not explicitly forbids unused resources. The closest thing I found is a statement:

This element contains a listing of the ontologies/resources referenced in the phenopacket.

in MetaData > resources explanation.

An unused resource should produce either error or warning. I think warning is more appropriate.

@julesjacobsen @pnrobinson any thoughts?

[pnrobinson]

A warning would be good. On the other hand, it might mean that somebody used a certain version of some ontology and did not find any matches, but still the ontology would belong in the metadata, so I am not sure it is even a warning.