set the label as display_name for obo-symbols.
return the query-hash, not its last element.
save entity/symbol only if it is not null.
add migration to update display-name for obo

The symbols of obo-ontologies need an update.
This also pertains to the generation of
the class-hierarchy tree.
obey hound.
Merge pull request #1105 from ontohub/592-obo_class_names

592 obo class names