Decrease CPU load caused by Draggable

The draggable control now only triggers dragging in case there is really a drag action. In case just a click is done
the control just pulls the draggable to the front if its not in the front already.
BringToFront-method for draggable and window

Both the draggable and the window control get a method that allows to move the control inside its parent to the front
 position so its rendered on top of its siblings.
Merge pull request #76 from mkaring/1.4

Decrease CPU load caused by Draggable