Implemented Request::getAcceptedContentTypes().

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

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

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.

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

use `getIs...` instead of `is...` to allow these methods to be used as
virtual properties.

This is forconsistency to the rest of the framework.
Only methods that take parameters may be named `is...`.