see https://github.com/yiisoft/yii2/commit/0cfd41a21a8d89cc577590a253893542e60d43ce#commitcomment-5238567
issue #2233

fixes #2233

- i18n now falls back to `en` from `en-US` if message translation isn't found
- View now falls back to `en` from `en-US` if file not found
- Default `sourceLanguage` and `language` are now `en`

fixed #1021

load extensions before preloading components to have aliases set for
extensions like debug module.

Moved Application::$controllerNamespace init into variable declaration, reordered Module::__construct.

when error occurs while handling errors output was not readable in web
context