Add support for shape-based testing of JSON-LD/OWL output

[gaurav]

We can use shape-based testing such as using ShEx or Shacl to make sure that JSON-LD/OWL generated by this library is described correctly. If existing shapes are available for OWL types such as classes, restrictions and instances, we could reuse those in this testing. The shapes we build for our own types could be reused in our other tools (phyloref/clade-ontology#65, phyloref/klados#83).

Note that we had an error caused by the type of an entity being set incorrectly (#33); to guard against some issues, shape-based testing should make sure that we detect the correct number of shapes in an input file.