• add shader variants for decal previewing
• start to add code for part icon
• refactor material properties to be serializable
todo:
• fix decal preview scale (need to call UpdateScale on detached state)
• fix texture preview in part icon
• adjust culling per-object when rendering (turns out cull and ztest values are used by unity at the render time, not by the shader itself, so they can be adjusted in material property blocks!)
