Add "deaccession" and "abort" functions

[mcampos-quinn]

Currently, there is no means to remove an asset from the repository beyond deleting the relevant AIP manually.

There should be a function to remove an asset and record it as deaccessioned in the pymm database.

Use cases for this would be a film that needs to be rescanned or a video that is transferred with different specs.

Similarly, a failed ingest results in some stub AIPs and corresponding database records. There should be a function to select such a stub and scrub all its object and event records (and log entries?) to start from scratch.

[kieranjol]

👀