Merge multi-touch gestures event branch

This is a squashed commit of the SOC2017_GESTURES branch from
https://github.com/prashantkn94/wxWidgets.git

Closes https://github.com/wxWidgets/wxWidgets/pull/551

include/wx/gtk/window.h

@@ -355,6 +355,16 @@ public:
 
     wxRegion             m_nativeUpdateRegion;  // not transformed for RTL
 
+#if defined(__WXGTK3__)
+    unsigned int         m_touchCount;
+    unsigned int         m_lastTouchTime;
+    int                  m_gestureState;
+    int                  m_allowedGestures;
+    int                  m_activeGestures;
+    wxPoint              m_lastTouchPoint;
+    GdkEventSequence*    m_touchSequence;
+#endif
+
 protected:
     // implement the base class pure virtuals
     virtual void DoGetTextExtent(const wxString& string,