Bulk-import with images already in Sipi

[subotic]

Use-case 1: Image is in Sipi and need to create knora-base:StillImageFileValue

Instead of providing <knoraXmlImport:file path="/usr/local/share/import-images/incunabula/12345.tiff" mimetype="image/tiff"/> allow to provide something like <knoraXmlImport:iiif path="incunabula_12345.jp2" mimetype="image/jp2" thumbX="88" thumbY="128"/> which should trigger a call to SIPI and retrieve all necessary information so that the two knora-base:StillImageFileValue instances.

Use-Case 2: Image is in Sipi and need only to link to an existing knora-base:StillImageFileValue

For Use-case 1 to work, Sipi will need to be able to store the necessary metadata, e.g., inside a sidecar file (dasch-swiss/sipi#254)

Needs #1110.

[benjamingeer]

Bulk import is being reimplemented in knora-py, which could also handle this use case.