draft idea of action based responses
implementation of Response tied to actions

Result of a discussion with @qiangxue
- there is not global Yii::$app->response anymore, every action has
  dedicated response class
- implementation allows using HMVC pattern now, nested actions do not
  interfer
Changed existing code to match the changes regarding response
Merge pull request #548 from cebe/action-response

implementation of Response tied to actions