Add Open Library ID code field

[xplosionmind]

As a step towards implementing #532, it would be really useful to connect books to the OpenLibrary catalogue by entering the OpenLibrary ID for each book.

This is a specific example of that requested in #112: linking the Inventaire entry to other catalogs across the web.

[jum-s]

This is already possible with the entities endpoint : https://inventaire.io/api/entities?action=by-uris&uris=isbn:9783882200041
Currently 800+ inventaire entities have an OLid property (P648), plus all wikidata items inventaire recognizes: for example, the 12000+ works with the same P248 property (ie: https://inventaire.io/api/entities?action=by-uris&uris=wd:Q109617045)

[maxlath]

This should have been solved by inventaire/inventaire-client#339

You should now find an OpenLibrary field in the entity editor: