BBB: pre-upload presentation slides

To support the presenters to prepare their BBB meetings a pre-upload for the presentation slides is implemented.

The presentation is uploaded in the BBB course element on the meeting date. As soon as the BBB room is opened (i.e. the session is available), the presentation is uploaded automatically to the BBB session and set as default presentation.

Formats to support: any office documents, PDF, jpg, jpeg, png

Total upload limit of all files per meeting must be configurable in administration --> BBB; Default: 100 MB.