Proposed new module type: minimal

Proposal:

A minimal module consists of:

* all rdfs:label annotation assertions between a named class and a literal
* all rdfs:subClassOf axioms between two named classes (`is_a` in obo)
* `SubClassOf(R some D)` where D must be a named class for some ontology-specific set of object properties R
* `Transitive(R)` for the same set of R
* Any declarations to support the above classes and R

The primary use case is an NCBITaxon minimal module that cuts down on size for basic consistency checking, with labels for human readability. But this is also useful for many other scenarios:

- relation graph closures
- most bioinformatics use cases e.g. with GO, UBERON, CL, MONDO

Minimal modules are not recommended for browsers. The lack of synonyms, text definitions, etc make them potentially confusing and misleading for many directly end-user facing tasks

The issue names no files, tests, or implementation entry points. Start by reviewing how existing module types are defined and extracted, then determine the scope and acceptance checks for a minimal module containing the listed ontology assertions and declarations.

Written by the indexing model from the issue text.