Add loading functions for more 3D pose frameworks

[niksirbi]

This is a replacement/generalisation for #124

We were originally using that issue to keep track of various 3D pose estimation frameworks we would like to potentially support, but then we converted that to an issue specifically for Anipose. Because that issue is being closed with #358, I'm opening this meta-issue to keep track of other 3D frameworks.

See also this related issue: #363

3D markerless pose estimation + tracking frameworks

• Load 3D pose data from Anipose #124
• DANNCE
• JARVIS see this manual
• Freemocap, see this discussion

Once we decide to tackle any particular item from the above list, it should be converted into its own issue.