Changed demos to delete the dock manager when the main window is closes to ensure that all floating widgets als "closed" (destroyed)

examples/sidebar/MainWindow.cpp

@@ -51,3 +51,13 @@ MainWindow::~MainWindow()
 {
     delete ui;
 }
+
+
+void MainWindow::closeEvent(QCloseEvent *event)
+{
+    QMainWindow::closeEvent(event);
+    if (m_DockManager)
+    {
+        m_DockManager->deleteLater();
+    }
+}