QmlDesigner.designDocumentController: fix for copy n paste

We have to clear the cache of the meta system.

Task-number:QTCREATORBUG-5578
Change-Id: I6f7a77609fb5535ade5925a405ae156edfee2b22
Reviewed-on: http://codereview.qt.nokia.com/2215
Reviewed-by: Thomas Hartmann <Thomas.Hartmann@nokia.com>

src/plugins/qmldesigner/components/integration/designdocumentcontroller.cpp

@@ -775,6 +775,9 @@ void DesignDocumentController::paste()
                 targetNode.nodeListProperty(defaultProperty).reparentHere(pastedNode);
             }
 
+            transaction.commit();
+            NodeMetaInfo::clearCache();
+
             view.setSelectedModelNodes(QList<ModelNode>() << pastedNode);
         } catch (RewritingException &e) { 
             qWarning() << e.description(); //silent error