Extruders model now listens to global container changed, instead of definition changed.

This solves issue where switching between machines with the same definition did not cause extruder materials to be updated

CURA-2493

cura/Settings/ExtrudersModel.py

@@ -50,9 +50,9 @@ class ExtrudersModel(UM.Qt.ListModel.ListModel):
 
         self._active_extruder_stack = None
 
-        #Listen to changes.
+        # Listen to changes.
+        UM.Application.getInstance().globalContainerStackChanged.connect(self._updateExtruders)
         manager = ExtruderManager.getInstance()
-        manager.globalContainerStackDefinitionChanged.connect(self._updateExtruders) #When the global stack changes to a printer with different extruders.
 
         self._updateExtruders()