Add drivetrain replay application

This adds a basic example application for replaying the 2019 drivetrain.

I also make it so that the LogReader will stop event processing once it
is done.

Change-Id: Icd0187f240191b8d23e31608eb6e5a5a49fd068c
diff --git a/aos/events/simulated_event_loop.h b/aos/events/simulated_event_loop.h
index db0b840..99450a3 100644
--- a/aos/events/simulated_event_loop.h
+++ b/aos/events/simulated_event_loop.h
@@ -71,6 +71,7 @@
 
   // Sets the simulated send delay for the factory.
   void set_send_delay(std::chrono::nanoseconds send_delay);
+  std::chrono::nanoseconds send_delay() const;
 
   // Returns the node that this factory is running as, or nullptr if this is a
   // single node setup.