Add deletes in ISN-specific initial state.

When performing an initial state based on a list of ISN's - typically the use case is to bring the target up-to-date for the listed records. Unfortunately, this synchronization will only work for inserts and updates - not for deletes. I suggest to add a parameter "send also deletes" to the IS definition - to send also information that an ISN in the list was not found in Adabas and should be deleted in the target.