Specular and fresnel effects in preview

The next development release of ModelConverterX contains improvements to the rendering of the object in the preview. The two biggest changes are that the specular hotspot and the fresnel effects are now shown in the preview as well. I am not convinced that the fresnel effect is exactly like in FSX, but I think it is rather close at the moment. Besides those two changes there are other smaller improvements as well, for example reflections work more like FSX now and also some additional material settings now have an effect in the preview.