Make language tags consistent

[cmungall]

Half the OBI definitions have lang=en, the others are plain literals/strings

➜  ontology git:(master) ✗ grep IAO_0000115 obi-edit.owl | grep -c lang=
656
➜  ontology git:(master) ✗ grep IAO_0000115 obi-edit.owl | grep -vc lang=
702

I don't think there is OBO guidance but I think intra-ontology consistency is always good, it seems your intent is to be explicit, I think it would be clearly safe to auto-convert all definitions to lang=en