set app as dock-less background tool

src/MainWindow.h

@@ -8,6 +8,7 @@
 #include <QMainWindow>
 
 class QSvgWidget;
+class QSystemTrayIcon;
 
 class MainWindow : public QMainWindow
 {
@@ -28,7 +29,10 @@ protected:
     void mouseReleaseEvent(QMouseEvent *event) override;
 
 private:
+    void setupTrayIcon();
+
     QSvgWidget *m_handleBar;
+    QSystemTrayIcon *m_trayIcon;
     QPoint dragPosition;
     bool dragging = false;
 };