Replace manual function calls to updateCurrentIndex with an explicit binding

This is mostly in support of Uranium PR #165 . That changes
SettingPropertyProvider so that the "properties" property does not
always change. However, in general this is the more correct approach.

Relates to CURA-2232

resources/qml/Settings/SettingComboBox.qml

@@ -87,34 +87,32 @@ SettingItem
         }
 
         onActivated: { forceActiveFocus(); propertyProvider.setPropertyValue("value", definition.options[index].key) }
-        onModelChanged: updateCurrentIndex();
 
-        Connections
+        Binding
         {
-            target: propertyProvider
-            onPropertiesChanged: control.updateCurrentIndex()
-        }
-
-        function updateCurrentIndex() {
-            // FIXME this needs to go away once 'resolve' is combined with 'value' in our data model.
-            var value;
-            if ((propertyProvider.properties.resolve != "None") && (stackLevel != 0) && (stackLevel != 1)) {
-                // We have a resolve function. Indicates that the setting is not settable per extruder and that
-                // we have to choose between the resolved value (default) and the global value
-                // (if user has explicitly set this).
-                value = propertyProvider.properties.resolve;
-            } else {
-                value = propertyProvider.properties.value;
-            }
+            target: control
+            property: "currentIndex"
+            value:
+            {
+                // FIXME this needs to go away once 'resolve' is combined with 'value' in our data model.
+                var value;
+                if ((propertyProvider.properties.resolve != "None") && (base.stackLevel != 0) && (base.stackLevel != 1)) {
+                    // We have a resolve function. Indicates that the setting is not settable per extruder and that
+                    // we have to choose between the resolved value (default) and the global value
+                    // (if user has explicitly set this).
+                    value = propertyProvider.properties.resolve;
+                } else {
+                    value = propertyProvider.properties.value;
+                }
 
-            for(var i = 0; i < definition.options.length; ++i) {
-                if(definition.options[i].key == value) {
-                    currentIndex = i;
-                    return;
+                for(var i = 0; i < control.model.length; ++i) {
+                    if(control.model[i].key == value) {
+                        return i;
+                    }
                 }
-            }
 
-            currentIndex = -1;
+                return -1;
+            }
         }
     }
 }