Changed view syncing to speed up save, delete, and backup (#7487)

- Renamed couch._sync_views to couch.sync_views.
- Changed couch._bulk_post_to to not rebuild views.
- Added explicit calls to couch.sync_views where needed.
- Improved error messages for caught exceptions in
  couch.process_deleted_docs.
- Made save_records sync views less often (Every 5K records)