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/config_flattener.cc b/aos/config_flattener.cc
index a9500e3..8018484 100644
--- a/aos/config_flattener.cc
+++ b/aos/config_flattener.cc
@@ -35,10 +35,10 @@
     }
   }
 
-  std::vector<aos::FlatbufferString<reflection::Schema>> schemas;
+  std::vector<aos::FlatbufferVector<reflection::Schema>> schemas;
 
   for (int i = 6; i < argc; ++i) {
-    schemas.emplace_back(util::ReadFileToStringOrDie(argv[i]));
+    schemas.emplace_back(FileToFlatbuffer<reflection::Schema>(argv[i]));
   }
 
   aos::FlatbufferDetachedBuffer<Configuration> merged_config =