title: Scroll TTreeView while dragging over/near the edges
body: <p>I have a TTreeView that can have lots of nodes, when a lot of nodes are expanded the tree uses a lot of screen space.</p>
  
  <p>Now suppose I want to drag a node that is near the bottom of the TreeView to the top, I can't physically see the top part of the TreeView because the node I am selecting is at the bottom. When dragging the node to the top of the TreeView I would like the TreeView to automatically scroll with me when dragging, by default this does not seem  to happen.</p>
  
  <p>A perfect example of this behaviour is seen in Windows Explorer. If you try to drag a file or folder, when you hover the dragged item (node) it automatically scrolls up or down depending on cursor position.</p>
  
  <p>Hope that makes sense.</p>
  
  <p>PS, I already know how to drag nodes, I want the TreeView to scroll with me when dragging if hovering near the top or bottom of the TreeView.</p>
  
  <p>Thanks.</p>