Abstract field import/export doesn't work for all formats

[dstillman]

Export to and import from Zotero RDF seem to work, though it tries to process both an 'abstractNote' and an 'abstract' field on import. (Also, should we use dc:description for abstracts instead and use fs:extra for the 'extra' field?)

Export to RIS doesn't include abstract.

Note: I'm now setting the abstract to item.abstractNote in toArray().

[dstillman]

(In [1171]) Removed abstract-as-note functionality in favor of a regular 'abstract' field

Abstract displays in metadata pane as a cropped one-line field by default; clicking the 'Abstract' label toggles between the cropped field and an expanded view

Some problems with import/export: https://www.zotero.org/trac/ticket/537

Refs #537

[simon]

(In [1251]) closes #537, abstract field import/export doesn't work for all formats

[dstillman]

(In [1252]) Addresses #537, Abstract field import/export doesn't work for all formats

Pushed updated BibTeX translators to repo

(Good to post-date the UTC timestamps by 15 minutes or so so that if I'm online I can just push them right away without updating the timestamps.)