removed the interface PrimitiveObject, since it isn't needed anymore, and just creates confusion, most of the methods are still in the respective subclasses, maybe they will be needed sometime...
made the filname argument more flexible, so that now every path is possible, the material file has to be in the same directory, like the obj file
fixed a warning and the rendering speed now doesn't shows the average rendering speed, but the actual speed(since last showing)
just a small fix, where the final rendering time wasn't right anymore