Allow multiple stage deadlines to be updated at once

In a situation where you have multiple stages that all have the same deadline, if you need to adjust the deadline it has to be done one stage at a time.

It would be great if Proof could work like Workfront tasks - an option to select multiple (or all) stages, then update the deadline once and each selected stage accepts the new date.

This should be either when first creating the proof, or for updating the workflow of an in-flight proof.