feat: add an option to show/hide navigator view

app/settings.h

@@ -25,6 +25,7 @@ public:
 
     static Settings *instance();
 
+    bool showNavigatorView() const;
     bool useLightCheckerboard() const;
     bool loopGallery() const;
     bool svgTiny12Only() const;
@@ -32,6 +33,7 @@ public:
     WindowSizeBehavior initWindowSizeBehavior() const;
     Qt::HighDpiScaleFactorRoundingPolicy hiDpiScaleFactorBehavior() const;
 
+    void setShowNavigatorView(bool on);
     void setUseLightCheckerboard(bool light);
     void setLoopGallery(bool on);
     void setSvgTiny12Only(bool on);