Translate unusable class expressions into placeholder classes

[balhoff]

If there is an axiom C SubClassOf (fatherOf some child) and (fatherOf only child), currently Whelk will throw out the whole axiom (same as ELK 0.4.3). But Whelk should be able to infer C SubClassOf (fatherOf some child) from this.

Similarly, Whelk should translate any minCardinality greater than 0 into someValuesFrom.