Change of fields 'model' and 'field_model'.

[bdgregg]

Change field_model to hold the term names/labels for both children and parents and drop the field 'model' entirely. No TID is needed in the sheet. Google Sheet ID for testing. Update README.md as well to reflect the change.

See lines ~839-849.

[bdgregg]

This will require a bit of re-work with adding a more generic get_taxonomy function to be able to pull any part of the taxonomy. With regards to models, these are the Islandora Models as referenced here: https://digital.library.pitt.edu/jsonapi/taxonomy_term/islandora_models. This contains (currently for us): Audio, Collection, Video, Digital Document, Paged Content, Page, Publication Issue, Compound Object, Newspaper)
This will also require a bit of re-work for the sheet-shucker script as it currently reads the "model" instead of the "field_model" field from the Google Sheet and inserts it into the 'model' field of the workflow_items table.