Rules for disease mappings

[matentzn]

1. We should prefer skos vocabulary over anything else (skos:exactMatch over owl:equivalentClass)
2. Every mapping_set must have resolvable mapping_set_id
3. mapping_set_ids defined at this mapping commons must adhere to this pattern for their ID:

http://w3id.org/sssom/commons/disease/[a-z][a-z0-9-]+.sssom.tsv

i.e. no underscores, upper case, or non-ascii characters in the id part.

To be continued