Curry item models in events for Draggables and Droppables

[billdami]

Right now the functionality of {{draggable-group}} and {{droppable-group}} are pretty bare-bones. They are good building blocks for more complex functionality, but on their own, they don't do much more than emitting the basic events when items are dragged and dropped.

One thing we can do to increase their usefulness is when events are emitted, instead of only sending an argument with the raw event to the action, also send along an optional "model" that is associated with the item that was dragged, dropped, etc.

For example:

<DroppableGroup
    @droppableActions={{hash
        dropped=(action "droppableDropped")
    }}
    as |Group|
>
    <Group.container as |Container|>
        <Container.dropzone as |Dropzone|}}
            <Dropzone.item @item={{item}}>{{item.name}}</Dropzone.item>
        </Container.dropzone>
        <Container.dropzone as |Dropzone|></Container.dropzone>
    </Group.container>
<DroppableGroup>

actions: {
    droppableDropped(event, item) {
        console.log(`The item/model that was dropped was ${item.name}`);
    }
}