Add button to autostrech for each file

stretchtoolbar.h

@@ -10,11 +10,13 @@ class StretchToolbar : public QToolBar
 {
     Q_OBJECT
     STFSlider *m_stfSlider;
+    QAction *m_autoStretchOnLoad;
 public:
     explicit StretchToolbar(QWidget *parent = nullptr);
 public slots:
     void stretchImage(Image *img);
     void resetMTF();
+    void imageLoaded(Image *img);
 signals:
     void paramChanged(float low, float mid, float high);
     void autoStretch();