code: public static String getDataTypeURI(String datatypeKey)
      {
      	Datatype datatype = getDatatype(datatypeKey);
      	return getOfficialDataTypeURI(datatype); 
      }
docs: Retrieves the unique (official) URI of a data type (example: "urn:miriam:uniprot").
  
  @param datatypeKey - ID, name, synonym, or (incl. deprecated) URI (URN or URL) of a data type (examples: "UniProt")
  @return unique URI of the data type
  
  @throws IllegalArgumentException when datatype not found