add owl:Ontology to uncefact and unlocode ontologies

[VladimirAlexiev]

It's common good practice to include descriptive metadata with each ontology.
It should include fields like:

• name
• description
• source
• last updated date

If you agree to do #187, the metadata could be like this (in turtle):

@prefix uncefact: <https://vocabulary.uncefact.org/uncefact/>.

uncefact: a owl:Ontology;
  rdfs:label "UNCEFACT Buy-Ship-Pay Reference Data Model";
  rdfs:comment "some nice long description";
  dct:source <https://unece.org/trade/uncefact/mainstandards>;
  rdfs:seeAlso <https://github.com/uncefact>, <https://vocabulary.uncefact.org/unlocode-vocab/>;
  dct:created "first publication date"^^xsd:date;
  dct:modified "last publication date, automatically updated"^^xsd:date.

And for UNLOCODE:

@prefix unlcdv: <https://vocabulary.uncefact.org/unlocode-vocab/>.
unlcdv: a owl:Ontology;
  rdfs:label "UNLOCODE geographic gazetteer";
  rdfs:comment "some nice long description";
  dct:source <https://unece.org/trade/uncefact/unlocode>;
  rdfs:seeAlso <https://github.com/uncefact>, <https://vocabulary.uncefact.org/uncefact/>;
  dct:created "first publication date"^^xsd:date;
  dct:modified "last publication date, automatically updated"^^xsd:date.