Add translator for LoC.gov entries

[AbeJellinek]

The Library of Congress has a few catalogs, but this is the main search portal for all of them. We bypass the Voyager 7 translator for lccn.loc.gov because of some problems running it within processDocuments, and we try to filter out direct links to non-catalog pages from search results.

Results won't actually be as nice as the tests until the MARC PR (#2576) is merged, specifically because of some incorrect logic that changed artworks to journalArticles.