Enhancements for withdrawal and returns

[mgesing]

• Display the shipping and delivery dates in the grid and on the edit page, along with whether the associated order has been canceled.
• The shipping and delivery dates should be included as Liquid placeholders in the message template ReturnCaseStatusChanged.CustomerNotification so that corresponding text can be dynamically shown or hidden.
• Add a new field called "IsCompleted". Set this to "True" automatically when the status is final (ItemsRepaired, ItemsRefunded, RequestRejected, Cancelled). An admin can reset this.