[x] Remove category assignments defined in relations, adding categories if they aren't on nodes yet
In Bioportal this applies for STY and Biolink, but that shouldn't always be expected
[x] Verify and update categories through OAK
Note that this functionality isn't fully implemented in OAK yet, so this is more of a stub for now
[ ] Check for existence of conflicting category assignments ( Holding off on this for now - see #7)