Use a Component for Explicit Spacers

A component has the advantage that the width property can depend from
other properties. This does not work with the previous on the fly
construction as the width does not update when the referenced property
changes.

clients/aurorae/src/qml/ButtonGroup.qml

@@ -22,7 +22,7 @@ Item {
             var component = undefined;
             switch (buttons.charAt(i)) {
             case "_":
-                var button = Qt.createQmlObject("import QtQuick 1.1; Item{ width: " + group.explicitSpacer + "; height: parent.height}", groupRow, "dynamicGroup_" + buttons + i);
+                component = explicitSpacerComponent;
                 break;
             case "A":
                 component = group.maximizeButton;
@@ -85,4 +85,12 @@ Item {
         }
         createButtons();
     }
+
+    Component {
+        id: explicitSpacerComponent
+        Item {
+            width: group.explicitSpacer
+            height: groupRow.height
+        }
+    }
 }