Add remote timestamps and queue_index to context

This gives us the knobs to expose the remote timestamps and queue_index
to anything receiving the events.  The first use case is the logger.  It
can now log forwarded entries *without* having to make the
message_gateway responsible for logging this data.

Change-Id: Ie34dd040d270f4fa90ecd6e463069e1adca1818a
diff --git a/aos/controls/control_loop-tmpl.h b/aos/controls/control_loop-tmpl.h
index f937bb4..349a55c 100644
--- a/aos/controls/control_loop-tmpl.h
+++ b/aos/controls/control_loop-tmpl.h
@@ -58,7 +58,7 @@
       // If the driver's station reports being disabled, we're probably not
       // actually going to send motor values regardless of what the FPGA
       // reports.
-      last_pwm_sent_ = robot_state_fetcher_.context().monotonic_sent_time;
+      last_pwm_sent_ = robot_state_fetcher_.context().monotonic_event_time;
     }
   }