Rename orderOptimizer to order_optimizer
Rename orderOptimizer to order_optimizer

As per our code style.

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