Support import of .hkx animations

[Jonahex]

[aerisarn]

@Jonahex the issue is that hkx is usually stripped of root motion data, so we need to add a way to import them. Maybe use hkAnno format?

[Jonahex]

When hkx animations need to be imported they usually don't have root motion. For my use cases it would be completely enough to add identity transform for root motion

[aerisarn]

Probably import plain and simple and then do an editor for root motion