Qt5.13 fix

Index: src/libkstapp/view.h
--- src/libkstapp/view.h.orig
+++ src/libkstapp/view.h
@@ -14,6 +14,7 @@
 #define VIEW_H
 
 #include <QGraphicsView>
+#include <QMenu>
 
 #include "kst_export.h"
 
