Improve Export Functionality of WebCube

The export-document functionality in webcube should be improved with the following two functions:

1. the ‘Export’ button summarises all selected documents in one PDF in the ‘Export as PDF’ format. This can certainly be interesting depending on the use case, but is not desired by us. It would be desirable to have both options here --> Export as PDF as individual documents or summarised in one PDF. Today, the only way to export as individual documents is to press the PDF button for all of them individually.

2. we would like to (optionally) select the download location to which the download should take place