Clean-up after import

[nilshoerrmann]

We are using XML Importer (integration) to regularly import a product database. The catalog changes seasonally, adding new and removing old products. While XML Importer does a great job adding new products it doesn't care about orphaned items: those still existing in Symphony but no longer in the import database.

In order to allow data synchronisation, it would be great, if XML Importer offered additional feature to remove entries after import. I'm thinking of a filter interface like the one used in the datasource editor, that allows filtering entries that should be deleted (select box values for example). The latest import date (modification date) could be used to match orphans.

The number of deleted entries could be added to the import status report:

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Creating the UI wouldn't be hard, because the code already exist in the core but I'm not sure how to handle the deleting process internally so I'm calling @brendo for input (and help).