wumpus-basic

Copperbox revision 1872.

File name changes - Basic.Graphic.Drawing becomes Basic.Graphic.Context function.

I still haven't worked out the new type of Drawings that represent Pictures with DrawingContext. Because TraceDrawings can produce empty lists of Primitives, Wumpus-Basic has a liftToPictureU operation (U - for unsafe) to get a Picture from a non-empty list of primitives, for pictures-in-context, I'm not sure if the picture should be wrapped with a Maybe instead.