controller improved

Some code cleanup, related with my comments:

- [one](https://github.com/yiisoft/yii2/commit/11bc899bc122e4ada5182f1066e4527ea912233e#commitcomment-5265568);
- [two](https://github.com/yiisoft/yii2/commit/11bc899bc122e4ada5182f1066e4527ea912233e#commitcomment-5265562);
- [three](https://github.com/yiisoft/yii2/commit/11bc899bc122e4ada5182f1066e4527ea912233e#commitcomment-5265603).