Add dance sequencer feature

[UuuNyaa]

A feature to create dance motions by placing dance elements on the timeline like a music sequencer.

TODO

• Survey existing implementations/applications
• Extracting dance elements from MMD motions

[UuuNyaa]

There is a possibility that Motion Editing can be used to achieve element transitions.
https://guytevet.github.io/mdm-page/

[UuuNyaa]

sample00.mp4

sample04.mp4