Refactored MysqlStorageManager

Could you make it more simple. Something like this:

```
$bindValuesArray = [
	['status', self::STATUS_NEW, \PDO::PARAM_INT],
	['limit', $count, \PDO::PARAM_INT],
];
if (!empty($documentType) && is_string($documentType)) {
	$documentTypeSQL .= ' AND `document_type` = :documentType';
	$bindValuesArray[] = ['documentType', $documentType, \PDO::PARAM_STR];
}
$sqlSelectForUpdate = sprintf('SELECT * FROM ' . $tableName . '
	WHERE `status` = :status %s
        ORDER BY `timestamp` ASC
	LIMIT :limit
	FOR UPDATE', $documentTypeSQL);
$statement = $connection->prepare($sqlSelectForUpdate);
foreach ($bindValuesArray as $bindValue) {
	$statement->bindValue($bindValue[0], $bindValue[1], $bindValue[2]);
}
```
...