Gui: Gesture: add option to disable tilt

On Qt5, using pinch will inevitably cause tilt. It's annoying, so it is disabled by default.

In the future, it's best to introduce some kind of threshold to overcome for the tilt to be triggered.

src/Gui/NavigationStyle.h

@@ -412,6 +412,7 @@ protected:
 
     bool thisClickIsComplex;//a flag that becomes set when a complex clicking pattern is detected (i.e., two or more mouse buttons were down at the same time).
     bool inGesture; //a flag that is used to filter out mouse events during gestures.
+    bool enableGestureTilt = false; //fetched from settings
 };
 
 class GuiExport OpenCascadeNavigationStyle : public UserNavigationStyle {