title: Qt - How to force the drop action to be copyaction when the drop location is some other application
body: <p>I have subclassed QMimeData and drag&amp;drop works perfectly fine within my widget – for both copyAction and MoveAction, Data gets copied and moved as needed (based on shift / ctrl keys etc.)</p>
  
  <p>For compatibility I am supporting other simple formats such as text/plain – the major problem is, I cannot allow ‘move’ operation for the drops to other applications for these compatible formats.</p>
  
  <p>For example, I allow my data to be dropped from my widget to some textbox – but only as long as it is a ‘copyAction’. But, I do not see any way of forcing this.</p>
  
  <p>Question: How to force the drop action to be ‘copy action’ for all external widgets, while allowing the copy/move within my widget?????</p>
  
  <p>By 'force' it is meant no matter what user chooses (ctrl, shift or whatever) - my data should always get 'copied' and not 'moved' when the drag happens for compatible formats. (while it should allow copy and move for its native format)</p>
  
  <p>How to enforce this in Qt?</p>