Playfield elements lose material when changing parameters.

[Pandelii]

Playfield elements use any materials that have been assigned to them when they are regenerated by moving points (walls, ramps), moving the element (flippers/bumpers), or adjusting parameters (bumpers, flippers).

Elements should not regenerate materials if a new material has been applied.

[freezy]

This is a symptom of the fact we don't yet store the actual Unity material, but still its VP presentation. A quick fix would be to not set the material when regenerating the mesh, but at some point we need to start dealing with Unity-generated materials and store them accordingly.