[NCBI PubMed] Multiple fixes and additions

- Books: fix authors, add call numbers, attach bookshelf links
- Add support for some bookshelf pages. Books/chapters that don't have a corresponding PMID are not supported until we can figure out how to get Book metadata from Book IDs.
- Tweak do/detectSearch. Attach chapters where available from doSearch.
- Don't support multiples in bookshelf search, because we don't support all books from individual pages.
- Add language to journal articles.
- Restructure code.
Merge pull request #555 from aurimasv/pubmed-fixes

[NCBI PubMed] Various improvements for books and journal articles