adjust class-hierarchy task for failureresilience

For now we just want to read the class hierarchy for
ontologies, which use URI-style class-names in sentences.
This change will add the ability to walk through the ontologies
and continuining if one fails (it provides some error output).
Merge branch 'augmenting249_display_symbols_as_dag' into develop
Merge branch 'develop' into develop.ontohub.org