citeproc-js relies on this in several locations. Seems that Zotero passes these IDs to citeproc from the item picker. We also need to consider existing embedded items in Word/LO documents, but they do have embedded URIs, so it shouldn't be a problem.
CC @fbennett
Add functions to generate sample data for various formats
* Zotero Web API JSON (Zotero.Item::toJSON)
* CiteProc-JS JSON
* Export translator JSON
* Direct serialization of Zotero.Item fields
Add a way to load sample data into DB from JSON
Add tests for loading sample data into DB
Add tests for automatically generated data
This will help us make sure that field mappings and data formats don't change
Also some support code that was useful here and will probably be
useful for other tests. This is a pretty complicated thing to test, but
it seems to work.