Add abstract support to translators

[dstillman]

Tracking ticket for using the data layer's new abstract note support in translators -- create individual tickets for the individual translators or just add a comment here if you're working on one.

Zotero.Notes.add(noteText, sourceItemID, isAbstract)

It'd be good to update at least a few of the translators to save abstracts by Beta 3 this Friday/weekend (e.g. PubMed, which should now create an abstract note rather than taking a snapshot of the abstract page).

minVersion should be changed to 1.0.0b3.r1 if not already.

[dstillman]

For Beta 3, would also be good to add N2 for RIS import (though, amazingly enough, not AB, according to the spec).

[simon]

(In [953]) addresses #427, Add abstract support to translators.

-translators may now attach abstracts simply by assigning a value to item.abstractNote
-added abstract support to PubMed translator

[simon]

(In [956]) addresses #427, add abstract support to translators

adds abstract support to JSTOR and ProQuest translators
adds abstract support to RIS translator
uses dcterms "abstract" property in Zotero RDF for abstract export