[*] BO : Allow complex GROUP BY in SQL Manager

Improved slightly the RequestSql class to allow GROUP BY to use some functions.

For example, this would not work on the current version : 
```sql
SELECT 
    DATE_FORMAT(`date_add`, '%m/%Y') as Mois, 
    SUM(shipping_cost_tax_excl) as `Frais de port HT`, 
    SUM(shipping_cost_tax_incl) as `Frais de port TTC` 
FROM ps_order_carrier 
GROUP BY MONTH(ps_order_carrier.date_add)
```
The GROUP BY MONTH(date_add) being the issue. This PR fixes it.