Yii2 And 'safe' Validator

Hi guys.

I miss ‘safe’ validator.

Sometimes I have very simple form (so only the ‘default’ scenario created by Model::scenarios() exists), but I need some custom attributes to be mass-assigned (btw one possible usecase for this is editing many-to-many relations with ActiveForm’s checkboxList)

Of course I can merge the result of parent::scenarios() with my custom attribute, but this is ugly.

Added SafeValidator. Thanks.