DolphinQt: Give hotkeys their own "background input" setting.

Source/Core/DolphinQt/Settings/InterfacePane.h

@@ -35,6 +35,7 @@ private:
   QCheckBox* m_checkbox_use_builtin_title_database;
   QCheckBox* m_checkbox_use_userstyle;
   QCheckBox* m_checkbox_show_debugging_ui;
+  QCheckBox* m_checkbox_focused_hotkeys;
   QCheckBox* m_checkbox_use_covers;
 
   QCheckBox* m_checkbox_confirm_on_stop;