[DragDrop] consider support GhostGUI and GhostOverlay for simple gui

[ivan-mogilko]

The primary reason why GhostGUI and GhostOverlay modes don't work for GUI and controls is that AGS does not provide means to copy any GUI or control's looks onto a sprite. And reimplementing gui drawing is a bad idea, at least in the context of this module.

However, there are couple of narrow cases when this might be feasible: GUI buttons with normal graphic, and empty GUIs with a sprite on background. In both cases it's a matter of pasting a sprite onto the ghost representation.

Might add a support for this.