added resolving of symlinks for recursive directories creation

Example of bug:
If you have a symlink for directory
/var/www/site.com/storage->/media/data
then this code will cause a exception:

```
FileHelper::createDirectory(Yii::getAlias('@app/storage/images'), true);
```

```
PHP Warning – yii\base\ErrorException
mkdir(): File exists
```

It whould be better to use `realpath()` for this.