Builder: Cleanup ir.attachment after deleting images (image, image-attachment etc)

[bobslee]

Images which afterward will be removed from the Builder Form, should be deleted from "ir.attachment" afterwards.

This prevents polution and orphanes in the "ir.attachment" table.

Current analysis:

1. Regarding Orbeon, there's no (HTTP)-request - to the Odoo persistence service - which handles the deletion of these images.
2. There's solely the (HTTP)-request /crud/orbeon/.../data.xml - Which for which images either exist or not in the data as URL-path.

A possible approach would be, to determine and delete the "ir.attachment" (images) for the Builder Form which don't exist in the (XML) data by URL mentoined above in bulletpoint 2.

It would also be a good idea to store the Orbeon control-/fieldname for the image on the "ir.attachment" model as well. Which could be implemented in the function handle_binary_data()