Fix alignment of models in the scene

[margaritaG]

There's a mismatch between the complete scenes generated with the current _generate_sceneobj.py code and the rendered RGBD images of the same scene.

Take scene val/0/942 (trajectory 2 from the validation set), this is the RGB rendering 6250.jpg:

And this is a screenshot of the rendered _completescene.obj for the same scene using the current code in _generate_sceneobj.py:

You can see that the x and y axes of the objects in the scene are misaligned between the two images. The reason is just a different assumption about the alignment of the models between the ShapeNet dataset and SceneNet code.

With this patch the result is instead:

which matches the RGB rendering from above.

[jmccormac]

Thank you very much for highlighting this Margarita. The original code actually works fine on the ShapeNet I had stored locally here from a while ago, but I just re-downloaded it to verify and the axis are indeed now swapped! This update will help any others who are downloading it new!