Scheduled Dispatch feature

Code is tested and run well on small-ish train network. Not tested extensively.

src/widgets/timetable_widget.h

@@ -34,6 +34,7 @@ enum VehicleTimetableWidgets {
 	WID_VT_EXPECTED_SELECTION,          ///< Disable/hide the expected selection button.
 	WID_VT_CHANGE_SPEED,                ///< Change speed limit button.
 	WID_VT_CLEAR_SPEED,                 ///< Clear speed limit button.
+	WID_VT_SCHEDULED_DISPATCH,          ///< Scheduled Dispatch button.
 };
 
 #endif /* WIDGETS_TIMETABLE_WIDGET_H */