Add CSV download for all admin backend tables

From #40 (comment 2875081540) by @wieland.mareike :

Also I'd like to discuss an export function, some easy csv export of all schedules surveys and their exact settings.

Regarding this point (and slightly at odds with #18), I'd like to suggest adding a [CSV] button to all displayed tables to trigger an in-browser compilation of the displayed information into a CSV file for download. Since the information is directly available from the backend, there might be no need for an "export" to be triggered.

I would assume that this could be implemented by either by retrieving the remaining rows from the API before CSV creation or switching to client side pagination for the admin backend.