independent flag for json structured logging

- logjson flag remove logformat flag
- passed to eth Config
- logsystem not a field of Ethereum
- LogSystem does not need to expose GetLogLevel/SetLogLevel
- message struct just implements more generic LogMsg interface
- LogMsg is a fmt.Stringer with Level()
- jsonMsg ([]byte) implements LogMsg
- remove "raw" systems
- move level logic inside StdLogSystem
- logsystems only print their kind of msg: jsonLogSystem prints jsonMsg, StdLogSystem prints stdMsg

cmd/ethereum/main.go

@@ -135,7 +135,7 @@ The Ethereum JavaScript VM exposes a node admin interface as well as the DAPP Ja
 		utils.JSpathFlag,
 		utils.ListenPortFlag,
 		utils.LogFileFlag,
-		utils.LogFormatFlag,
+		utils.LogJSONFlag,
 		utils.LogLevelFlag,
 		utils.MaxPeersFlag,
 		utils.MinerThreadsFlag,