Load COB and cob-to-external

[cmungall]

First request is to load cob.owl

I think this should be not negatively affect anything. Recall the main COB release is rewired to use COB IDs where appropriate:

https://obofoundry.org/COB/using-cob/

I would also like to load cob-to-external. there are 2options:

1. the main cob-to-external.owl file, which is a mix of logical axioms and skos annotations (the latter used when we cannot make a LA due to discrepancies)
2. the above with equivalencies removed

2 may be preferable to avoid needless is-a self-loops and bringing in COB classes that are already covered by OBOs