Implement start order logic to provide 'list' of known riders to start ID unit

[boons605]

• Racetracker to remove a rider that has started from the start ID unit
• ID units to emit event that there are no known riders
• IStartOrderManager to respond to this event and send new rider when start order is important or send the entire list of known riders when start order is irrelevant. Decide if new heat is started automatically or user interaction is required.