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/y2019/wpilib_interface.cc b/y2019/wpilib_interface.cc
index 097f011..b6d432f 100644
--- a/y2019/wpilib_interface.cc
+++ b/y2019/wpilib_interface.cc
@@ -661,7 +661,7 @@
     // Flash the red light slowly.
     StatusLightT color;
     if (!status_light_fetcher_.get() ||
-        status_light_fetcher_.context().monotonic_sent_time +
+        status_light_fetcher_.context().monotonic_event_time +
                 chrono::milliseconds(100) <
             event_loop_->monotonic_now()) {
       color.red = 0.0;