Implement deformation plots

[martinal]

Just need to

• [ ] Add a channel "deformation"
• [ ] Map that to a vertex texture
• [ ] If provided, add deformation to coordinates in vertex shader

This should work fine in concert with most if not all other methods.

[martinal]

For most purposes, just setting mesh.points to x0 + deformation should do the trick.

[martinal]

Added example of how to do that to demo notebook.