Increment layer count for each object that should be printed as a single object
Increment layer count for each object that should be printed as a single object

This makes the ordering for one-at-a-time mode more clear

CURA-222 #Start-Review

markwal/CuraEngine,markwal/CuraEngine,Ultimaker/CuraEngine,ROBO3D/CuraEngine,Ultimaker/CuraEngine,pratikshashroff/pcura,totalretribution/CuraEngine,pratikshashroff/pcura,ROBO3D/CuraEngine,totalretribution/CuraEngine,alephobjects/CuraEngine,markwal/CuraEngine,alephobjects/CuraEngine,alephobjects/CuraEngine,pratikshashroff/pcura,totalretribution/CuraEngine,ROBO3D/CuraEngine