#13 Migrate from ADODB to PDO

Related to the issue #13

I have implemented this for use PDO. It doesn't have compatibility with adodb but can coexist with the old model.

Just extends from DatabaseModel and thats all.
It work almost like the other one, with the LoadBalancer, the debug and that kind of things, just change the method to access like PDO.
Query, prepare and execute, in addition of affectedRows and lastInsertId .

Do you think that it's a good approximation?