Make parent item information visible.

Don't know if you're interested in this but this will make the parent item information visible in the "Copy Info" tab for each item. Parent items are listed in a select with the current item and any child item removed from the list.

Any current relationship will be removed prior to the new relationship being added if the item id or instance number don't match.

I needed the ability to retroactively add parent relationships and couldn't find anywhere to do that, hence this patch.