transaction callback added

Added transaction callback shortcut . Related with [this](https://github.com/yiisoft/yii2/issues/3384) issue 
Look at this example:

```php
function someComplicatedWrapper()
{
	$db->transaction([$this, 'updateArticles']);
}

function anotherComplicatedWrapper()
{
	$db->transaction([$this, 'updateArticles']);
}

function updateArticles($db)
{
	// ....	
}
```