Get CUDA/OpenGL interop

[Teja10]

Change renderer.cu to properly swap the Optix image with an OpenGL framebuffer, and modify render_test.py to use OpenGL for rendering. You will need to figure out how to load GL functions on the C++ side.

[crozhon]

See branch sdl for a rough outline.

I didn't use interop, just copied the buffer back to CPU, then used glBufferData to move it back to GPU.

[crozhon]

I edited it again to do interop now - was pretty simple. Not sure what happens to PyTorch image I create each time though. Maybe that's the memory leak?