Add convenience function to handle multiple experiments at once

[JuliaSprenger]

At the moment only a single experiment can be downloaded via the API. We could provide a method that permits to download multiple experiments at once and tries to merge those into a single (csv?) file. @killianrochet I think you started looking into something like this already, right?

[killianrochet]

Hello @JuliaSprenger yes, I've started looking, the only problem I can see is that in order to download an experiment, you need the ID of the experiment, so you need to find a way of getting the ids of the experiments you want to download in a user-friendly way.