Results 4 issues of justYuMu

FlutterBugly.checkUpgrade(isManual: false, isSilence: true); 在App启动时, 检查更新, 期望是不弹toast提示. 在debug包下是生效的,不弹提示. 但是在 release 包会提示,"当前已是最新版本"

添加type字段, 判断是c2c会话还是分组会话; 添加messageId, 防止本地消息列表数据重复

ethereum github [Add 'txHash' field to the result of 'accounts.signTransaction'](https://github.com/ChainSafe/web3.js/pull/2694); And i can get txhash before sendTranasction() with go-ethereum sdk. i want know how to get txhash with web3dart before...