Implemented Request::getAcceptedContentTypes().

This reverts commit 9d7597d6, reversing
changes made to 6b6390f7.

implementation of Response tied to actions

Renamed some folders to fit changed app structure.

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

in UploadedFile::loadFilesRecursive
fixes #542

fixes #544

renamed Application::handle() to handelRequest()

Name make more sense imo as it is not clear what it handles otherwise.
Removed unused method processRequest form console app and also refactored
console Application to be more similar to web Application.

* 'master' of github.com:yiisoft/yii2:
  Removed unused namespace.
  Put back Yii::getObjectVars() and fixed infinite loop in Object::toArray().
  Recursively return previous exceptions in toArray().
  Added previous exception in toArray().
  Removed headers in ErrorHandler.

fix MigrateController

Added support for different response formats.
Support for error response in different formats.