This reverts commit a5846fa2, reversing
changes made to 2a6e064a.

MimeTypeController generates a map of file extensions to MIME types

It uses `mime.types` file from apache http located under
http://svn.apache.org/viewvc/httpd/httpd/trunk/docs/conf/mime.types?view=markup

This file has been placed in the public domain for unlimited
redistribution,
so we can use it and ship it with Yii.

see also yiisoft/yii#2851 and yiisoft/yii#2857

Fixed the bug that requesting protected or private action methods would cause 500 error instead of 404

typo

Obsolete keys searching isn't work when we have serveral categories for tranlation with DbMessageSource. Obsolete array filled with last message category only, because it'll always overwritten.

fixes #3578