fix: retrieve all layer_height and layer_height_0 settings from meshgroup or global settings (CURA-956)
fix: retrieve all layer_height and layer_height_0 settings from meshgroup or global settings (CURA-956)

ROBO3D/CuraEngine,Ultimaker/CuraEngine,totalretribution/CuraEngine,alephobjects/CuraEngine,totalretribution/CuraEngine,ROBO3D/CuraEngine,ROBO3D/CuraEngine,totalretribution/CuraEngine,alephobjects/CuraEngine,alephobjects/CuraEngine,Ultimaker/CuraEngine