Add wxWindow::EnableTouchEvents()

Don't request touch event generation for all windows by default, this
has an inherent overhead and is not needed for 99% of the application
windows, so require calling EnableTouchEvents() explicitly to do it
instead.

Note that this requires properly initializing gesture recognizers in
wxOSX now that they're not always allocated, otherwise releasing them
when destroying the window would crash.

include/wx/gtk/window.h

@@ -77,6 +77,9 @@ public:
     virtual bool Reparent( wxWindowBase *newParent ) wxOVERRIDE;
 
     virtual void WarpPointer(int x, int y) wxOVERRIDE;
+#ifdef __WXGTK3__
+    virtual bool EnableTouchEvents(int eventsMask) wxOVERRIDE;
+#endif // __WXGTK3__
 
     virtual void Refresh( bool eraseBackground = true,
                           const wxRect *rect = (const wxRect *) NULL ) wxOVERRIDE;