Fix item duplication bug that can occur (due to virtual dom change tracking…

Fix item duplication bug that can occur (due to virtual dom change tracking mixups and jQuery UI draggable clone)

drag_and_drop_v2/public/js/view.js

@@ -127,7 +127,9 @@
             h(
                 'div.option',
                 {
-                    key: item.value,
+                    // Unique key for virtual dom change tracking. Key must be different for
+                    // Placed vs Unplaced, or weird bugs can occur.
+                    key: item.value + (item.is_placed ? "-p" : "-u"),
                     className: className,
                     attributes: attributes,
                     style: style