revert: remove auto long image mode

- remove auto long image mode.
- there is no "auto" requirement for this.
- user can utilize fit by height/width to achieve the same goal by manually click them.
- some optimization code about graphic view are preserved.

app/graphicsview.h

@@ -39,17 +39,12 @@ public:
     void displayScene();
     bool isSceneBiggerThanView() const;
     void setEnableAutoFitInView(bool enable = true);
-    void setLongImageMode(bool enable = true);
 
     bool avoidResetTransform() const;
     void setAvoidResetTransform(bool avoidReset);
 
     static QTransform resetScale(const QTransform & orig);
 
-    // Long image mode support
-    bool isLongImage() const;
-    void fitLongImage();
-
 signals:
     void navigatorViewRequired(bool required, QTransform transform);
     void viewportRectChanged();
@@ -75,7 +70,6 @@ private:
     // ... or even more? e.g. "fit/snap width" things...
     // Currently it's "no fit" when it's false and "fit when view is smaller" when it's true.
     bool m_enableFitInView = false;
-    bool m_longImageMode = false;
     bool m_avoidResetTransform = false;
     bool m_checkerboardEnabled = false;
     bool m_useLightCheckerboard = false;