title: Make jQuery sortable items droppable to their peers
body: <p>I have a sortable list (of tasks). It helps prioritize tasks, so I want to keep this functionality. Now I want to add subtasks to the functionality: I want to enable users to drag one task over to another task and drop it there to turn it into a subtask. </p>
  
  <p>Applying .draggable() and .droppable() to items that are already sortable has no effect. What could I do?</p>