feat: implement configurable font settings for VTK viewports and GUI elements with persistent preferences.

app/gcompose/src/MainPanel.h

@@ -12,6 +12,7 @@ namespace uLib {
     class ObjectsContext;
     namespace Vtk {
         class ObjectsContext;
+        class ViewportProperties;
     }
 }
 
@@ -40,6 +41,7 @@ private:
     ContextPanel* m_contextPanel;
     uLib::ObjectsContext* m_context;
     uLib::Vtk::ObjectsContext* m_mainVtkContext;
+    uLib::Vtk::ViewportProperties* m_viewportProps;
 };
 
 #endif // MAINPANEL_H