callable scenarios for actions: create, update, delete

[siggi-k]

callable scenarios for actions: create, update, delete

/**
 * @var string|callable
 * string - the scenario to be assigned to the model before it is validated and saved.
 * callable - a PHP callable that will be executed during the action.
 * It must return a string representing the scenario to be assigned to the model before it is validated and saved.
 *  The signature of the callable should be as follows,
 *  ```php
 *  function ($action, $model) {
 *      // $model is the requested model instance.
 *  }
 *  ```
 */
public $scenario = Model::SCENARIO_DEFAULT;

[cebe]

Thank you!