Exclude certain headings from being fetched

[sandbergja]

We may not wish to fetch all matching records from DLC. For example, we have changed "Illegal Aliens" to "Undocumented immigrants" in our local catalog, so we would not want to re-fetch DLC's problematic record. We also might not want to fetch a bunch of "Fictitious character" LCSH records, since they may be replaced with NARs soon.

Maybe this could be a command line argument that accepts a regex of headings to exclude.