Add WARC file support to IngestFiles and WarcbaseResourceStore

Re. IngestFiles: As you will see, I opted only to store WARC "response" records in the database, and not "request" or "metadata" records. Also, I didn't make use of WarcRecordUtils.getWarcResponseMimeType() because for it to be useful would have required too much copying of buffers. 

Re. WarcbaseResourceStore: Record-type detection could be more sophisticated (do we care about older WARC versions? error handling?).  

The only pertinent commits here are 4239f1f and 724eed2.