[Gui] allow to specify font for NaviCube

- the problem is that depending on the OS, the font of the NaviCube is hardly readable. For example under Windows 11, there is no Helvetica font and therefore an ugly replacement font is used. On some laptop screens the font is too large or too small etc.
- as solution this PR add the change the NaviCube's font and font size

- the PR also fixes an issue that the position (corner) of the NaviCube was not respected when the NaviCube is recreated. This fix is necessary for the PR therefore included

- as by-product the PR fixes #8082 since every change in the preferences now properly recreates the NaviCube

- the PR also removes the strange and unused class "HuuhaaClassPy"

src/Gui/View3DInventorViewer.cpp

@@ -1176,6 +1176,23 @@ NaviCube* View3DInventorViewer::getNavigationCube() const
     return naviCube;
 }
 
+void View3DInventorViewer::createNavigationCube()
+{
+    if (!naviCube) {
+        naviCube = new NaviCube(this);
+        naviCubeEnabled = true;
+    }
+}
+
+void View3DInventorViewer::deleteNavigationCube()
+{
+    if (naviCube) {
+        delete naviCube;
+        naviCube = nullptr;
+        naviCubeEnabled = false;
+    }
+}
+
 void View3DInventorViewer::setAxisCross(bool on)
 {
     SoNode* scene = getSceneGraph();