Mapping stages from disease table in CDA

[pnrobinson]

1. See file OpDiagnosisMapper
2. Create TSV file with Stage terms (e.g. https://ontobee.org/ontology/NCIT?iri=http://purl.obolibrary.org/obo/NCIT_C27966) -- limit to "generic" stage terms such as Stage III.
3. Consider how to model this with the MapEntry class -- do we need a class hierarchy (because right now the labels of the "neoplasm_types.tsv" file are hard coded)
4. Add this to OpDiagnosisMapper and then add the Stage to the Disease entry in Phenopacket.

[ielis]

Update, the stage mapping is the sole responsibility of oncoexporter.cda.mapper.OpDiseaseStageMapper.