[System Tray] Call Qt.createComponent for PlasmoidItem only once

I slapped a console.time in there and it would show 1ms even on some
of the subsequent invocations, so while QML engine should do some
caching magic, calling it once is better anway.

Differential Revision: https://phabricator.kde.org/D2719

applets/systemtray/package/contents/ui/main.qml

@@ -46,6 +46,8 @@ MouseArea {
 
     property alias statusNotifierModel: statusNotifierModel
 
+    property Component plasmoidItemComponent
+
     function updateItemVisibility(item) {
 
         //Invisible
@@ -86,8 +88,10 @@ MouseArea {
     }
 
     Containment.onAppletAdded: {
-        var component = Qt.createComponent("items/PlasmoidItem.qml")
-        var plasmoidContainer = component.createObject(invisibleEntriesContainer, {"x": x, "y": y, "applet": applet});
+        if (!plasmoidItemComponent) {
+            plasmoidItemComponent = Qt.createComponent("items/PlasmoidItem.qml");
+        }
+        var plasmoidContainer = plasmoidItemComponent.createObject(invisibleEntriesContainer, {"x": x, "y": y, "applet": applet});
 
         applet.parent = plasmoidContainer
         applet.anchors.left = plasmoidContainer.left