Support for own DibiDriver

Add support for own DibiDriver placed in different place than native drivers.

```php
$driver = new Vendor\Libs\Dibi\Drivers\DibiPdoDriver();
$connection = new DibiConnection(array(
	'driver' => $driver,
	'dsn' => 'oci:dbname=//server.domain:1521/database',
	'username' => 'username',
	'password' => '********',
	'lazy' => TRUE,
));
```