Extract response generator from ErrorCatcher middleware

[olegbaturin]

Move ErrorCatcher logic to ErrorResponseFactory.
https://github.com/olegbaturin/yii3-error-handler/blob/error-response-factory/src/ErrorResponseFactory.php
https://github.com/olegbaturin/yii3-error-handler/blob/error-response-factory/src/Middleware/ErrorCatcher.php

Add ErrorResponseFactoryInterface, so application can implements own ErrorResponseFactory, and ExceptionResponder middleware with custom exception parsers can become a part of ErrorResponseFactory.
https://github.com/olegbaturin/yii3-app-api/blob/master/src/Renderer/Error/ErrorResponseFactory.php

[samdark]

Good idea. Want to make a pull request?

[vjik]

Done by #133