Support for axiom annotations

[NicolasRouquette]

OWL2-DL allows axioms to have zero or more annotations, see:
https://www.w3.org/TR/owl2-syntax/#Annotations_of_Ontologies.2C_Axioms.2C_and_other_Annotations

There is no such support in OML.

In particular, this prevents using annotations for modeling quantities and units.

currently, we can only annotate quantities/units on the definition of a scalar property, e.g:

https://github.com/NicolasRouquette/metrology-vocabularies/blob/vim4/src/examples/oml/example.org/some-domain.oml

  @rdfs:label "mass.basic"
  @vim4-annotations:generalQuantity "http://iso.org/iso-80000-4.1#mass"
  @vim4-annotations:measurementUnit "http://iso.org/iso-80000-4.1#kilogram"
  scalar property mass.basic [ domain Component range xsd:double functional ]

But we cannot annotate value assertions:
https://github.com/NicolasRouquette/metrology-vocabularies/blob/vim4/src/examples/oml/example.org/test-property-values.oml

  ci camera1 : some-domain:Component 
  [ some-domain:name "camera1" 
    some-domain:mass.basic "0.31"^^xsd:double
    some-domain:mass.allocation "0.5"^^xsd:double ]

It would be useful to have syntax support for annotating value assertions, e.g. :

  ci camera1 : some-domain:Component 
  [ some-domain:name "camera1"
    @vim4-annotations:measurementUnit "http://iso.org/iso-80000-4.1#kilogram"
    some-domain:mass.basic "0.31"^^xsd:double
    @vim4-annotations:measurementUnit "http://iso.org/iso-80000-4.1#kilogram"
    some-domain:mass.allocation "0.5"^^xsd:double ]