Chemical Laytime Calc should allow changes to the laytime calc when invoice is in pending state

Today the Chemical Laytime Calculator (laytime_c) doesn't allow you to change the laytime calculation when you have a demurrage invoices in status pending.

You are required to delete the demurrage invoice before you can make the changes to the laytime calculation.

When you delete this invoice you also delete the history for your Invoice Actions under the Receivable Summary List, which is not ideal.

The nature of a demurrage invoice is that it is being challenged by the customer and therefore changes to the laytime calculation happens in almost all cases after the issuing of the first demurrage invoice.

It is far from ideal that the workflows associated to the Chemical Laytime Calculator and the Invoice Actions under Receivable Summary List are not compatible, and Veson should seek a "bugfix" for this that allow you to make changes to a laytime calculation when the associated demurrage invoice is in pending state (meaning that you of course have to reverse this invoice first).