Timetable auto separation is now per vehicle, with a company default.

Remove global on-off setting.
Add button to timetable GUI.
Add company setting to control default for new vehicles.

Fix automate, start date, change time and autofill buttons
being shown enabled for other companies' vehicles.

src/vehicle_base.h

@@ -54,6 +54,7 @@ enum VehicleFlags {
 	// Additional flags not in trunk are added at the end to avoid clashing with any new
 	// flags which get added in future trunk, and to avoid re-ordering flags which are in trunk already,
 	// as this breaks savegame compatibility.
+	VF_TIMETABLE_SEPARATION = 14,///< Whether the vehicle should manage the timetable automatically.
 	VF_AUTOMATE_TIMETABLE = 15, ///< Whether the vehicle should manage the timetable automatically.
 };