Fix up XmlMaterialProfile::serialize so we can properly serialize duplicated materials
Fix up XmlMaterialProfile::serialize so we can properly serialize duplicated materials

We now use GUID to look up all containers belonging to a material. In
addition, we handle the multiple containers better

Contributes to CURA-342

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