feat: add an option to show/hide bird-eye view (#180)

app/settingsdialog.h

@@ -25,6 +25,7 @@ private:
     QCheckBox * m_stayOnTop = nullptr;
     QCheckBox * m_useBuiltInCloseAnimation = nullptr;
     QCheckBox * m_showTitleBar = nullptr;
+    QCheckBox * m_showBirdEyeView = nullptr;
     QCheckBox * m_useLightCheckerboard = nullptr;
     QCheckBox * m_loopGallery = nullptr;
     QCheckBox * m_autoLongImageMode = nullptr;