Add a delay before marking items as read

[r-thomson]

In the Mail app on iOS, there is a small delay (roughly a half second) after opening an unread email before it’s actually marked as read. I always thought this was a nice touch for when you accidentally tap the wrong email before quickly swiping back. It’s also nice when using the up/down arrows to quickly flip through emails looking for a certain one.

It would be nice to see NetNewsWire implement the same behavior. Right now if I accidentally open the wrong item (especially with the left/right swipe gesture, which I tend to do accidentally while scrolling), I have to remember to re-mark the item as unread before going back, or I might “lose” that item.