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.
While we're changing this. instead of the messy xpath, let's use something like
```
var tabs = doc.getElementsByClassName('tabContent');
var root;
for (var i=0; i<tabs.length; i++) {
  if (tabs[i].offsetHeight) {
    // visible
    if (Zotero.isBookmarklet && tabs[i].id != 'allResults-content') return false;

    root = tabs[i].getElementsByClassName('resultListContainer')[0];
    break;
  }
}

if (!root) return false;

var results = ZU.xpath(root, './/a[contains(@class,"previewTitle") or contains(@class,"resultTitle")]');
```