transaction callback added

Added transaction callback shortcut . Related with [this](https://github.com/yiisoft/yii2/issues/3384) issue 
@qiangxue 
>Note that within updateArticles() you may not want to use transaction.

any reason for this? usually you should use it there, but if you have some custome code to wrap it in also in method that call `updateArticles` you should start another transaction. So it is not a valid use case as for me, any other valid use cases ? )