Add support for the new OpenPose BODY_25 model

This adds support for the new BODY_25 model from OpenPose.

PLEASE NOTE: If a model is missing in this map, the whole component does not work even though OpenPose could handle it. Additionally it crashes with a super obscure error message a la exception at map::at (not more info, no stacktrace, nothing). Maybe consider parsing the input with OpenPose's op::flagsToPoseModel (like you already do in some places anyway) and get rid of this map.

PLEASE ALSO NOTE: I did not change the default, even though it might be a good idea because the setup script provided with VisionX does not download any models besides BODY_25. So either consider changing the script, or use the new model.