More replay preparation.
 * Implemented closedListeners in Archiver.
 * Added some descriptions to timber.proto.
 * Logserver will not attempt to send "sync" messages to it's handlers. These should be ignored.
 * MetadataHandler no longer writes a new file on startup, but will according to design only append if the file exists.
 * TimberClientPipelineFactory now holds only one instance of TimberClientHandler, so shutdown is called on the same instance which is started.