Simplified _zoteroFieldMap for citeproc-js

[fbennett]

Citeproc-js doesn't have a general mechanism for representing short forms in item input, but follows the current convention of using a journalAbbreviation item field for the short form of container-title, and a shortTitle field for the short form of title. To get current (Zotero 2.0) behavior, it is enough to just map these field through to the item; the processor will handle the rest.

This permits the _zoteroFieldMap object to be indifferent to "long" and "short", and handle only adjustments to item field names. The attached patch applies this change.

A more robust (but still experimental) mechanism for short forms is available in the processor, based on abbreviation lists. That will (or rather would) require additional infrastructure in Zotero, and possibly some adjustment to the distribution of work between the calling application and the processor. If implemented, it can play nice with the existing shortTitle/journalAbbreviation mechanism; I think this patch won't cause any exceptional hassles.

[simon]

(In [6315]) closes #1699, Simplified _zoteroFieldMap for citeproc-js (thanks to Frank)