Improving drag and drop

- No longer rendering the task view to another drag view, instead we 
  drag the task view directly.  This allows us to do a smooth transition
  to and from the freeform workspace and the stack by animating the 
  thumbnail scale as we clip/unclip the task view.
- Removing the extra code to disable rotation while dragging since the 
  system does that for us already

Change-Id: I1e02c9319347aace9870eaa4983b3b87c5f0f58e