Update animation action api usage for modern blender

[RichardPerry]

This addon borrowed some of the logic for retrieving and setting root bone data from a target bone (hips typically from mixamo animations) from an older addon built to work with blender's old runtime properties API. However outside of custom user properties, animation data can no longer be accessed this way.

For the addon to work with blender 5.0 and certain versions of 4.x it needs to be re-written taking into account these changes: https://developer.blender.org/docs/release_notes/5.0/python_api/#blender-50-python-api.

In particular, the fucntions that access fcurves properties such as the copyHips function need to be reworked.