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/aos/BUILD b/aos/BUILD
index beeb2b0..4ccfd0e 100644
--- a/aos/BUILD
+++ b/aos/BUILD
@@ -596,3 +596,9 @@
         "//aos/testing:googletest",
     ],
 )
+
+py_binary(
+    name = "flatbuffers_static",
+    srcs = ["flatbuffers_static.py"],
+    visibility = ["//visibility:public"],
+)