Ensure that Alice pays for cancelled arrangement period

[tuxxy]

Let's say Alice creates an arrangement for 20 Ursulas.

Alice decides she doesn't like a particular Ursula storing a KFrag the same period that she publishes an arrangement and wants to specifically revoke that KFrag.

We should ensure that Alice pays for the period that she revokes on. If she revokes on day 0 of the arrangement, she should pay for day 0.

[michwill]

I think, this is how it works. Although, I'd let @szotov to confirm that

[vzotova]

Alice can revoke fee only for next periods. Payment for first/current period (0 day) will be irrevocable.

[michwill]

So, she gets refunded only for future periods? Sounds good to me