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/command_type.h

@@ -326,6 +326,7 @@ enum Commands {
 	CMD_SET_VEHICLE_ON_TIME,          ///< set the vehicle on time feature (timetable)
 	CMD_AUTOFILL_TIMETABLE,           ///< autofill the timetable
 	CMD_AUTOMATE_TIMETABLE,           ///< automate the timetable
+	CMD_TIMETABLE_SEPARATION,         ///< auto timetable separation
 	CMD_SET_TIMETABLE_START,          ///< set the date that a timetable should start
 
 	CMD_OPEN_CLOSE_AIRPORT,           ///< open/close an airport to incoming aircraft