Rename skin_outline_count to wall_line_count
Rename skin_outline_count to wall_line_count

CURA-2724

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