Reflect any mappings currently in Python code in terminology server or model

[turbomam]

For example, there are mapping statements using skos predicates for several terms, but not cancer stage observation types.

See also cancerDHC/example-data#31

[gaurav]

I feel like this issue should be moved to the ccdhmodel repo: those mappings (or their documentation, or a link to their documentation) ought to be in the model. Is there a reason we should tackle this in the Example Data repo?

[turbomam]

I agree about moving to ccdhmodel.

[gaurav]

Could you please start making a list of these terms in this issue? Even once we end up with exemplar CRDCH datasets in the Example Data repo, I suspect that it won't be easy to find them all when we need them. It would also be useful to see if they are grouped in any particular way.