Fixing ProQuest search, widening ebrary's domain

ProQuest search results now include ebrary e-books in an extra tab. Zotero scrapes were returning everything regardless of which tab was visible, and these extra items caused the ProQuest translator to crash.

This fix changes the scrape results based on which tab is visible (database results or e-books), excludes some invaild sidebar links from the results, and calls the ebrary translator to handle ebrary e-book results. The ebrary translator was updated to handle links that come from ProQuest.
I don't think it's necessary at all. I actually did want to remove that line, though I left it in because I was trying to be conservative with my changes (particularly since I'm rather new to the Zotero codebase). I figured it'd get brought up if it was superfluous and unnecessary after all. And since it is, I'll excise it.