Setup initial qt plugin demo

include/rqt_demo_plugin/rqt_demo_plugin.hpp

@@ -0,0 +1,41 @@
+#pragma once
+#include "rqt_gui_cpp/plugin.h"
+#include <QtGui>
+#include <QtQuick>
+#include <QtWidgets>
+#include <qfileinfo.h>
+#include <qobjectdefs.h>
+#include <qpushbutton.h>
+#include <qquickview.h>
+#include <qquickwindow.h>
+#include <qresource.h>
+#include <qurl.h>
+#include <qwidget.h>
+
+inline void initResources() { Q_INIT_RESOURCE(res); }
+inline void cleanupResources() { Q_CLEANUP_RESOURCE(res); }
+
+namespace mg {
+
+class DemoPluginMg : public rqt_gui_cpp::Plugin {
+  Q_OBJECT
+public:
+  DemoPluginMg();
+  ~DemoPluginMg();
+
+  virtual void shutdownPlugin() {
+    RCLCPP_INFO(node_->get_logger(), "The plugin has been shutdown");
+  }
+  virtual void initPlugin(qt_gui_cpp::PluginContext &);
+};
+
+inline void DemoPluginMg::initPlugin(qt_gui_cpp::PluginContext &pc) {
+  QQuickView *qv = new QQuickView(QUrl("qrc:/qml/helloworld.qml"));
+  qv->setResizeMode(QQuickView::ResizeMode::SizeRootObjectToView);
+  QWidget *qw = QWidget::createWindowContainer(qv);
+  pc.addWidget(qw);
+
+  RCLCPP_INFO(node_->get_logger(), "The plugin has been initialized");
+}
+
+}; // namespace mg