Plan for new dnd interfaces

DragContext()

• creates store context

// For making things interactive

DragSource() => { } makes it draggable

• is type
• this.onDragStart() // return props
• updates context
• cb this.onDrop();

DropTarget() => { responds to events, makes it droppable

• accepts type
• cb this.onDrop();

// For attaching drag state to props

DragSourceMonitor() => { isDragging() getItemType() getItem() }

DropTargetMonitor() => { } isOver() isCompatableTarget()

DragLayerMonitor() => { isDragging() getItemType() getItem() }

// Misc data structure related things

accepts: [Symbol('foo')]

context = { active: sourceId, sources: [{isDragging}], targets: [{isOver}] };