Add optional table that tracks deleted entries

[svniemeijer]

In order to allow synchronisation of other catalogues with a muninn catalogue we need to keep track of which entries got deleted (and when), so we can inform the other side which entries they need to remove as well (since their last update point).
Instead of keeping the full metadata with a 'deleted' flag, it will be much more efficient to just keep a separate table for deleted entries containing only the UUID and metadata_date fields, since those are the only fields that we need for the synchronisation.

Having such a 'deleted' table needs to become an optional property of an archive (disabled by default).

The muninn-remove command then needs to be updated to also create an entry in the 'deleted' table when a product is removed.

We might also want to have some kind of muninn-query version that allows querying of entries in the 'deleted' table.

[svniemeijer]

We might want to keep the product_type and product_name fields as well, since these provide the alternative way of uniquely identifying an entry (besides the UUID)

[svniemeijer]

We should also make querying for any metadata changes fast. This means that the uuid and metadata_date should ideally be stored in a single table for both existing and deleted products.

This means that it may be more useful to capture the 'deleted' status using a new core property (have non-core namespace entries, tags, and links removed on a delete, but keeping a stripped down version of the core entry).