Improve imports of external classes & relations

[StroemPhi]

At the moment the import strategy I used was a mixture between using the MIREOT Protégé and copying between ontologies in one workspace. This can lead to missing metadata and axioms, is not a good practice.

Instead there should be something like:

• [ ] an aeon-core.owl containing only AEON core classes with external (BFO/IAO/OBI) parents
• [ ] an aeon-external.owl containing only the reused external classes
• [ ] an aeon-mappings.owl containing alignment with other ontologies and schemas using skos:exact/broad/narrowMatch from which a R2RML might be derived. The aeon-mappings.owl is probably best generated using SSSOM and ROBOT

[StroemPhi]

For having proper release artefacts that are obo compliant see also: https://github.com/INCATools/ontology-development-kit/blob/master/docs/ReleaseArtefacts.md#release-artefact-2-full-required