Images are not embedded when exporting a wiki page to an office format

When exporting a wiki page that contains images to an office format like ODT all the images are broken: they point to a file in the file system instead of being embedded in the office document. The path the images point to is correct on the server side, but the users download only the office document, without the external image artefacts. We should automatically embed images before serving the office document to the client.