This MR adds the possibility to upload material for contributions. The uploaded material will also be shown as session material and I implemented some shortcuts for upload and download of the material.
Event organizers must enable the upload for the contribution participants, e.g. at https://hcdc.hereon.de/datahub/events/data-science-symposium-7/edit/
Presenting authors (and session conveners or event organizers) find then an upload button next to their card
and they find it in the sidebar of their contribution