Fix function declarations.

#3215 

This PR changes the function declaration of ``excluded_paths()`` to match the function inherited from the class ``space_type_purl`` in which this function is declared as static. In ``space_type_purl.inc`` we have:

```php
  /**
   * Return an array of paths from which the space should never be active.
   */
  protected static function excluded_paths() {
    return array('features', 'features/*', 'admin', 'admin/*');
  }
```