feat(ossie): explain ontology and mapping documents on import

[obolonsky-owox]

Why

Apache Ossie recently split its Flights example into three documents (apache/ossie#458): flights.ontology.yaml (business concepts), flights.semantic_model.yaml (datasets) and flights.mapping.yaml (ontology ↔ semantic model). The canvas imports semantic models only. Importing the ontology from GitHub failed with "This file isn't an Ossie model". That message is misleading: the file is Ossie, just not a semantic model.

What

• parseOssie now names the document type when there are no datasets:
  • Ontology (ontology: list, also the legacy combined flights.yaml): "This is an Apache Ossie ontology (business concepts), not a semantic model. The canvas imports semantic models: import the file with a top-level "datasets" list instead."
  • Mapping (concept_mappings: list): "This is an Apache Ossie mapping document, not a semantic model. Import the semantic model it points to instead: ./flights.semantic_model.yaml" (from semantic_model_ref.iri, capped at 200 chars; generic hint when it is missing).
  • Anything else keeps "This file isn't an Ossie model".
• detectModelFormat routes pasted text with a top-level ontology / concept_mappings key to the Ossie reader, so pasting gets the same message instead of an empty OKF import.
• ossie-format.md: a paragraph on ontologies and mappings not being imported yet, and which Flights example files work.

Importing ontologies as conceptual models is a possible follow-up once the ontology spec settles.

Tests

• okf: ontology, legacy combined file, mapping with and without semantic_model_ref, generic fallback; detection of pasted ontology/mapping text.
• web: ontology via file upload and via paste shows the message.
• Ran the four real Flights files from apache/ossie main: the semantic model imports (6 marts); the other three show the new messages.
• okf 167/167, web 726/726, server 65/65, tsc --noEmit clean.

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