Provide a single download link for all exercise data

[ioalexei]

Various feedback/suggestions:

• Add one download link incl. All needed files for one exercise on top and not one link for each file
• When preparing for the session, I was in a middle of 2 choices. (1) I would like to make use of only data package for all exercises. This should help to make the flow easier for participants to follow, they don't have to keep downloading new data packages for every exercise, and of course save time. (2) I followed the materials.
  (1) is my preference, but I went for (2) as we are piloting the platform in this phase. I think we can add in the exercise estimate time to finish it?
• Is there a link where people can download all the exercises at once at the start of the training? downloading a different zip file each time is a bit unwieldy
  • Might be worth introducing drag-and-drop file loading and also adding a folder to a project – e.g. if learners download a zip of all training data at the start and add the folder to favourites in the browser, save some time from people trying to find the right files for each exercise