Babylon file creation from prims

The babylon file format groups objects together by parent ID. This is usable for multi-prim objects. However, we still have to deal with viewer faces that can have different materials assigned.

Looking at the file structure, exporting for every individual prim is relatively straightforward: For every prim:

• Collect all vertices for all faces
• Collect all indices for all faces
• Collect all normals for all faces
• Collect all UVs for all faces

Then for each prim:

• Create a new entry in meshes
• Give each prim mesh a unique ID
  • Calculate the djb2 hash of the shape
  • Calculate the djb2 hash of the materials
  • Create the ID from those
• Export all vertices (as "positions")
• Export all normals (as "normals")
• Export all UVs (as "uvs")
• Export all indices (as "indices")
• Export all materials (as "materials")

For each face:

• Create a new multimaterial
• Add the material for each face to the multimaterial
• Create a new submesh
• Add the face vertices/indices to the submesh