Switch magic timestamp channel to RemoteMessage

In order to track reboots and such, we really need to communicate more
information from the message_bridge to the logger.  It is a shame to
have to modify the MessageHeader to do this, even though it would be
nice.  Switch the remote timestamp channels over to a new RemoteMessage
channel instead, and add code to rename the channel when replaying.

There are no known log files with a MessageHeader actually logged, so
most of this should be pretty safe.  I've tested this on an old log file
by hand.

Change-Id: If81b31869b95040151d833d20ec3eb8623ab1cd4
diff --git a/third_party/flatbuffers/BUILD b/third_party/flatbuffers/BUILD
index 57f2b8e..ed39893 100644
--- a/third_party/flatbuffers/BUILD
+++ b/third_party/flatbuffers/BUILD
@@ -7,6 +7,7 @@
 exports_files([
     "LICENSE",
     "tsconfig.json",
+    "include/flatbuffers/reflection.bfbs",
 ])
 
 # Public flatc library to compile flatbuffer files at runtime.