extension of schemas for classical commentaries

[mromanello]

Hello @e-maud @simon-clematide 🙂 (and ping @sven-nm)

In our Ajax Multi-Commentary project we starting to use the impresso text-importer + JSON schemas to convert the OCR of our commentaries into a canonical format, from which then other various formats can be rebuilt.

The very first thing that needs to be adapted are the JSON schemas. We will need an equivalent of the newspaper issue schema for each commentary (our atomic document unit), while the commentary page schema will require only minor adaptations (compared to the newspaper page schema). Overall, this extension will help us think how to make these impresso schemas more generic in the future.

We will make our changes (additions) in a branch of this repository, and then later on we can discuss with a PR how to better integrate our schemas with the others.