Atto does not listen to the drop event

If I drag and drop image or text in atto and then save the form, the textarea content does not get saved.
This happens because Atto does not update textarea content on drag&drop event.

To reproduce:

1. Open a form that does not have required fields, for example, edit section summary
2. Drag and drop either text or image from another application into the atto editor
3. Do not do anything else, just save the form
4. The dragged content does not get saved