title: Clearing/resetting a model in qt (removing all rows)
body: <p>I'm confused about the correct way to reset or clear the data associated with a <code>QAbstractItemModel</code>.</p>
  <p>I'm writing an application in which the user can &quot;start over&quot; with a new set of data (empty, or small).</p>
  <p>Should I be deleting the old model when the user makes this request? Or should I leave the model alone and just remove all of the rows?</p>
  <p>Regards,
  Dan O</p>