Remove extruder creation logic from manager
Remove extruder creation logic from manager

This logic is now in cura/Extruder.py.

Contributes to issues CURA-1278 and CURA-351.

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