Add missing PMIDs by looking up DOI, create pubMedRequest.js

If the PMID is missing but the DOI is present, use the DOI to lookup
the PMID and PMCID with pubMedRequest

Creates lib/pubMedRequest.js which requests an object from PubMed's
API, and sanity checks the response.

Corrects testJSON input file in lib/zotero.js

Assorted code styling improvements

Bug: T1088
Change-Id: If174e13c124eb2c0f0e3582175167b5757c6912d