Fix QML warnings due to depricated on<signal> calls in Connections

As of 5.12, the signals used in connections should not be declared as on<signal>, but as
function on<signal>(arguments).

resources/qml/Settings/SettingExtruder.qml

@@ -24,7 +24,7 @@ SettingItem
         Connections
         {
             target: extrudersModel
-            onModelChanged:
+            function onModelChanged()
             {
                 control.color = extrudersModel.getItem(control.currentIndex).color
             }