This patch adds initial support for SKOS taxonomies as a
hierarchy-enabled alternative to UCO's current string-vocabularies
practice.

While the typical SKOS namespace is prefixed, the import of SKOS is
done by referencing an OWL-DL compatible subset of SKOS as a version IRI
import.  (See SKOS Reference C.3.)

Paul Brandt identified the SKOS strategy used in this patch, though his
initial draft was in another repository.  I ported the property to UCO's
ontology repository due to needing to satisfy references for SHACL.

This patch is a reduction from the first definition of
`core:TaxonomicConcept` drafted for UCO CP-99.

References:
* [OC-140] (CP-99) UCO should provide a SKOS taxonomy of device types
  for observable:deviceType
* #363
* https://www.w3.org/TR/skos-reference/#namespace-documents
  Section C.3, "SKOS RDF Schema - OWL 1 DL Sub-set (informative)"

Co-authored-by: Paul Brandt <paul@brandt.name>
Signed-off-by: Alex Nelson <alexander.nelson@nist.gov>

Dublin Core's `dcterms:FileFormat` class is an existing class that
represents file formats, including but not limited to IANA Media Types.
(The reference to IANA Media Types is found on the `dcterms:format`
property, where the IANA list is recommended, but not required.)

`dcterms:FileFormat` is defined as an `rdfs:Class`.  In order for UCO,
as an OWL ontology, to use this class as a range of a property
(especially `observable:mimeType`), it needs to be designated as an
`owl:Class`.

Note there are some things this patch does not do:

* This patch does not import Dublin Core.  It appears Dublin Core's
  model is incompatible with OWL 2 DL.  For instance, the property
  `dcterms:format` appears to violate the OWL 2 DL separation of
  datatype properties (range of literals) from object properties (range
  of objects), on review of its sub-property `dcterms:extent` having a
  range of literals.
* This patch does not extend `FileFormat`'s superclasses to also be
  OWL Classes.
* This patch does not adapt the `dcterms:format` property noted above,
  because in addition to its OWL 2 DL compatibility issues, its semantic
  scope extends beyond data formats.

Compatibility notes:

Extending `dcterms:FileFormat` to be both an OWL Class and RDFS Class is
compatible with OWL 2 DL.  Reviewing this record:
https://www.w3.org/TR/2012/REC-owl2-mapping-to-rdf-20121211/#Parsing_of_the_Ontology_Header_and_Declarations
Table 5
Row 2

An ontology that also designates `dcterms:FileFormat` as an `rdfs:Class`
would have the pair of `owl:Class` and `rdfs:Class` statements reduced
to `owl:Class` only as part of its OWL parse.

If an ontology has chosen to import Dublin Core as a whole, it has
already implicitly made a commitment to use OWL 2 FULL instead of
OWL 2 DL.

References:
* #363
* https://www.dublincore.org/specifications/dublin-core/dcmi-terms/#FileFormat
* https://www.dublincore.org/specifications/dublin-core/dcmi-terms/#format

Signed-off-by: Alex Nelson <alexander.nelson@nist.gov>

For compatibility with other graph data models that use IANA Media
Types, the required range is set to `dcterms:FileFormat`.

References:
* #363

Signed-off-by: Alex Nelson <alexander.nelson@nist.gov>

This patch adds a class hierarchy to distinguish between known IANA
Media Types and Media Types known to not be registered with IANA.

A unit test is added to demonstrate how mimeType being objects can also
enable hierarchical searches, even between IANA and non-IANA types.

A follow-on patch will generate validation result files.

References:
* #363

Signed-off-by: Alex Nelson <alexander.nelson@nist.gov>

References:
* #363

Signed-off-by: Alex Nelson <alexander.nelson@nist.gov>

…feature

A follow-on patch will generate a Make-managed file.

References:
* #363

Signed-off-by: Alex Nelson <alexander.nelson@nist.gov>

References:
* #363

Signed-off-by: Alex Nelson <alexander.nelson@nist.gov>