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

app/settings.h

@@ -37,6 +37,7 @@ public:
     bool stayOnTop() const;
     bool useBuiltInCloseAnimation() const;
     bool showTitleBar() const;
+    bool showBirdEyeView() const;
     bool useLightCheckerboard() const;
     bool loopGallery() const;
     bool autoLongImageMode() const;
@@ -49,6 +50,7 @@ public:
     void setStayOnTop(bool on);
     void setUseBuiltInCloseAnimation(bool on);
     void setShowTitleBar(bool on);
+    void setShowBirdEyeView(bool on);
     void setUseLightCheckerboard(bool light);
     void setLoopGallery(bool on);
     void setAutoLongImageMode(bool on);