Update \Gasoline\Mode\Base::to_form_element to support more types

Now supports types 'radio', 'checkbox', and 'select'
Update package gasform to cc1f10e
Update package gasform to 3aab55e
Major improvement to module auth
Fix bug in \Gasoline\Model\Base::to_form
Update \Gasoline\Validation::_validation_exists

Now returns true (validation passed) if value is null