Determine overlaps with OBO

 1. Figure out how much overlap there is between CCO and OBO (either OBO-Core or specific domain ontologies)
 2. Come up with a strategy: equivalence axioms vs ceding by one side

 * [ ] CORE: only matches I see are document & plan
 * [ ] ENVO: https://github.com/EnvironmentOntology/envo/issues/625