Drag n Drop support #22
Description
Drag'n drop will work for floating windows in the first implementation.
A FloatingWindow can be dragged when the mouse is pressed anywhere over its DragHandle (an arbitrary region over the component configured by the user) region.
On the drag event the window should be repositioned and its bounds checked with other floating windows.
Related to #23 which will use this
Depends on #24 since it will introduce the layerable stack