Venue: Custom Max Papers shouldn't allow more than one edge with the same head and tail

[melisabok]

This is to avoid PCs creating duplicated quotas by mistake.

I remember that using maxReplies = 1 validates this, @celestemartinez can you confirm that?

[celestemartinez]

Yes, maxReplies=1 should be enought to make sure PCs can't post multiple edges and they edit the existing ones.