Improve data dictionary and FAIRness

[iamleeg]

Data dictionary should:

• be available in some machine-readable format (maybe an XML schema definition or something)
• describe/link to standard formats for fields where they are used (e.g. ISO 3166-1 country codes, ISO 8601 dates)
• use standard formats for fields where standards exist (e.g. symptom ontologies; also for Pango lineage should capture the version of Pango)