Allow to globally disable the kill button

(only needed in swift pilot client so far)

src/blackgui/overlaymessagesframe.h

@@ -52,6 +52,9 @@ namespace BlackGui
         //! Show the inner frame
         void showStatusMessagesFrame();
 
+        //! Show kill button
+        void showKillButton(bool killButton);
+
         //! Hide the inner frame
         void hideStatusMessagesFrame();