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.cc b/aos/events/simulated_event_loop.cc
index 1dfb3af..bfe0de7 100644
--- a/aos/events/simulated_event_loop.cc
+++ b/aos/events/simulated_event_loop.cc
@@ -467,6 +467,10 @@
   }
 }
 
+std::chrono::nanoseconds SimulatedEventLoopFactory::send_delay() const {
+  return send_delay_;
+}
+
 void SimulatedEventLoop::MakeRawWatcher(
     const Channel *channel,
     std::function<void(const Context &channel, const void *message)> watcher) {