Improved `yii\helpers\Inflector::slug` to support more cases for Russian, Hebrew and special characters

Fixes #3687: Default `sourceLanguage` and `language` are now `en-US` in order for i18n formatter to work correctly

Fixes #3716: `DynamicModel::validateData()` does not call `validate()` if the `$rules` parameter is empty

Fixes #3715: Fixed the bug that using a custom pager/sorter with `GridView` may generate two different pagers/sorters if the layout configures two pagers/sorters

Support contribution credits updated

[ci skip]

issue #3520

Edited Asset Bundle PHP doc header information.

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