[Annotations] Empty PCR file created automatically after adding a new reference

[pafonta]

Steps:

1. Click on the Zotero menu, then on Add reference.
2. Create a new reference (tested with one with an UNPUBLISHED ID).
3. An empty PCR file is created in the local repository folder.

This is an implementation logic, neither a bug nor a feature. However, this could lead to misunderstanding for the user of NeuroCurator (UI) and NAT (annotations).

NeuroCurator: Why nobody in my curation team has the PDF of a reference in grey (ie. no PDF has been submitted to the localization server)?

NAT: Why is there empty PCR files in the corpus of annotations?

The goal would be to have an other implementation logic which doesn't rely on these empty PCR files.

NB: The row added in the References (Zotero) tab has therefore the color (grey) of references having been added to the "curator database".

[pafonta]

Also, double-clicking on a reference with an UNPUBLISHED ID and coloured white creates an empty PCR file.