On new, moved and renamed, and modied bags. indexer script should compare the bag's checksum with one in index

[mjordan]

The watcher script should use the bag's checksum to confirm that it is dealing with the same bag file in its on_moved() method.

[mjordan]

The checksum should be compared for new bags as well. Logic is:

• If a bag with the new bag's checksum doesn't exist, add the bag.
• If a bag with the new bag's checksum exists, update its bag_location_exact and bag_location fields, and its document_timestamp.

For moved or renamed bags, the logic is:

• If a bag with the moved or renamed bag's checksum exists, update its bag_location_exact and bag_location fields, and its document_timestamp. Do not update its ID.
• If a bag with the bag's checksum does not exist, add it as new.

For modified bags (bags that overwrite existing bags), the logic is:

• If a bag with the modified bag's checksum exists, update its bag_location_exact and bag_location fields (if necessary), its bag_hash value, and its document_timestamp. Do not update its ID.
• If a bag with the bag's checksum does not exist, add it as new.