Rewrite object export system

It has grown overly complicated.
Stuff to handle in better ways:

• Instances (from shared meshes, dupli groups, particle/hair duplis)
• Tracking of which LuxCore objects and shapes belong to which Blender objects (extra objects/shapes spawned from one Blender object, e.g. hair, particles, multi-material objects etc.)
• Pointiness (this is an intermediary shape)

It would be great if the new system could handle all that in a way that is easier to understand and more elegant.
For example, if an object is both visible in the scene as a normal object and used in a particle system, it would be great if the mesh was only exported exactly one time. So we need robust caching between the multitude of possible instancing options.

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