Show the selection rectangle from DF in Stonesense

[realSquidCoder]

It is theoretically possible to read the selection bounds from DF in Stonesense and show that info

[realSquidCoder]

To do this you would need to use DFHack::Gui::getDesignationCoords() and DFHack::Gui::getMousePos()

[realSquidCoder]

but wait until after #205 is done