add descriptions, update flasgger endpoints

fda-units-service/app.py

fda-units-service/onto_feat.py

fda-units-service/us-yml/getconcept.yml

fda-units-service/us-yml/ontologies.yml

fda-units-service/us-yml/ontology.yml

fda-units-service/us-yml/ontologybyname.yml

fda-units-service/us-yml/suggest.yml

fda-units-service/us-yml/validate.yml