Fix generator problem when using with namespaces

Generator falls with error when generating admin module for model with namespaces defined.
It should use `getClassName()` instead of `getPhpName()` in this case:

Sample `schema.yml`:
```yaml
propel:
  _attributes:
    package: lib.model.Acme.Model
    namespace: Acme\Model
  article:
    id: ~
    title: varchar
```

```php
$map->getClassName(); // \Acme\Model\Article
$map->getPhpName(); // Article
```