Add ability to explicitly assign mesh warp(s) to each point in a model

[adamkewley]

The model warper currently figures out which mesh warps are associated with which points by looking at which geometries are attached to the same base frame as the point.

It's a generally-useful heuristic because usually points are spatially close to the body they're attached to (usually). However, it's problematic when:

• There's multiple meshes attached to that frame and it wouldn't necessarily make sense for the engine to combine those meshes into a single warp kernel
• The point is actually closer to the surface of some other mesh attached to some other base frame (think: points that are between two bodies or similar

So the engine needs to support users manually specifying point-to-warp associations in the .warpconfig.toml file, such that they can decide how these cases will be handled. I'm thinking something like:

[points]
[[point_name]]
associated_meshes = ['pelvis.obj', 'femur.vtp']

The engine would then read this at initialization time and use it when fetching (+creating) the associated warp kernel that's needed for that particular point.