Added new feature to store logs into database.

- added new configuration for database.
- added new method LoggingAction() into ExampleController class.
- added new atribute "$_log" into Controller class.
- now the Dao class use PDO::FETCH_ASSOC when call to fetchAll in doSelect() method.
- new core class Log. This class add support to store logs into database.
- added a bit of css into layout/default.phtml.
- added new class LogDao, to get the logs from database.