BibFormat: several bibreformat optimisations

• Optimises queries that fetch updated records. Uses last_updated technique like the other daemons (indexer, ranker). (closes #1106)

• Improves concurrency of bibfmt queries. All queries modifying bibfmt are set to low priority to prevent the locking problem with MyISAM:
  • a long select comes from bibreformat to check formats that need updating;
  • a small insert or update or delete comes from bibupload;
  • all subsequent selects are blocked. With LOW_PRIORITY, the update/delete/insert query will wait till all the selects are done before trying to acquire a lock.

• Range queries for missing formats to not block bibfmt. A single JOIN was taking too long as it does have to analyze at least a million of rows. The query is now split in chunks.

Co-authored-by: Tibor Simko <tibor.simko@cern.ch>