Add the missing handling when user selects a different machine

So far, the case that a user selects a different machine, was not handled
yet.

refs #881

src/blackgui/components/hotkeydialog.h

@@ -88,6 +88,7 @@ namespace BlackGui
             void ps_combinationSelectionChanged(const BlackMisc::Input::CHotkeyCombination &combination);
             void ps_combinationSelectionFinished(const BlackMisc::Input::CHotkeyCombination &combination);
             void ps_changeSelectedAction(const QItemSelection &selected, const QItemSelection &deselected);
+            void changeApplicableMachine(int index);
             void ps_accept();
 
             void synchronize();