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/events/logging/log_cat.cc b/aos/events/logging/log_cat.cc
index c146945..9c75076 100644
--- a/aos/events/logging/log_cat.cc
+++ b/aos/events/logging/log_cat.cc
@@ -62,7 +62,7 @@
             // replaying it.
             std::cout << channel->name()->c_str() << ' '
                       << channel->type()->c_str() << " at "
-                      << context.monotonic_sent_time << ": "
+                      << context.monotonic_event_time << ": "
                       << aos::FlatbufferToJson(
                              channel->schema(),
                              static_cast<const uint8_t *>(message))