Improved bodypix single pose example

[cansik]

As already discussed in #389 this PR adds the following improvements to the single pose example:

• removed yolox example code
• added strides parameter to avoid onnx dependency if not needed
• added DirectML and CoreML execution providers for onnxruntime
• added openvino support as runtime alternative (and a --runtime argument)
• added upscaling of keypoints and masks to the size of the input image (if it does not match the input size)
• removed duplicate indices from resulting keypoints list

Maybe it makes sense to extract the methods and libraries into a util module to not have duplicate code in the single- and multi-pose example. For now, this PR already helps to run the models on the CPU (and MacOS / Windows) as well.

[PINTO0309]

Thanks for the great pull request!