Multiple clicks leads to multiple empty typesetting rounds being created

[mauromsl]

when a user clicks the "New typesetting round" button multiple times, it can lead to multiple empty rounds being created. This may happen whenever the server is too slow to respond, or the user is facing connectivity issues slowing the request/response cycle.

We could avoid this by ensuring no new rounds can be created when a given round has no tasks associated with it. Additionally, we can use the ConfirmableForm that comes with backend validation. The requirement of the backend validation of the user confirmation should avoid multiple chained requests being processed