Speed up building of the layerdata mesh
Speed up building of the layerdata mesh

Use numpy copies rather than python iteration since it is far faster.

Contributes to CURA-224

senttech/Cura,totalretribution/Cura,markwal/Cura,Curahelper/Cura,hmflash/Cura,fieldOfView/Cura,ynotstartups/Wanhao,ynotstartups/Wanhao,hmflash/Cura,fieldOfView/Cura,markwal/Cura,Curahelper/Cura,totalretribution/Cura,senttech/Cura