WasVisible: query visibility of scenes and shapes, RobustNegativeScale: support light

[DP News-Robot]

You can easily query whether the scene or shape was (potentially, at least partially) visible in the last rendering event. This accounts for both frustum culling and occlusion culling. Use , for this. Demo is in examples/viewport_and_scenes/test_was_visible. See forum thread for history behind this feature. You can use TCastleRenderOptions.RobustNegativeScale to make lighting work correctly even …