Minimal fix for #2092

This removes the modal for drops and throws it into a Growl notification instead. Absolute minimal fix for issue #2092, and has much room for improvement:

The message is kinda verbose to read in the time it's visible, so I'd love to instead have "You found an item!" with a picture of the specific drop. But I'm having a devil of a time getting a dynamically-formed icon style to show up in the notification... I can get one to show up if I manually specify it, but none of the dozen methods I tried for splicing in the type and key of the drop worked.