Fixes #5494: Added support for specifying a menu header as a configuration array in `yii\bootstrap\Dropdown`

Fixes #6345

Fixes #6367: Added `yii\gii\generators\crud\Generator` to support customizing view path for the generated CRUD controller

Fixes #4395: Added `$checkAjax` parameter to `yii\web\Response::redirect()` to support default redirection behavior for AJAX/PJAX requests

Fixes #5070: Gii controller generator should use controller class name instead of controller ID to specify new controller

fixes #5503

The exceptions thrown on error are db exceptions.

Works around PHP Bug https://bugs.php.net/bug.php?id=68528

fixes #5962

introduced by @samdark in the following commits:

- c6b0e24a
- 7c5938f9
- eaf8ece5

Added relative time translations

Fixes #5480: Added defensive code to `yii\web\User::getIdentity()` to avoid potential infinite recursion

fixes #6263 and has no problem with PHP Bug:

> it is a PHP bug: https://bugs.php.net/bug.php?id=45543
> Fixed in this commit: php/php-src@22dba2f#diff-7b738accc3d60f74c259da18588ddc5dL2996
>
> Fixed in PHP >5.4.26 and >5.5.10. http://3v4l.org/mlZX7

Fixes #4277: `yii\grid\GridView` is no longer throwing an exception in non-debug mode when results are empty and `columns` aren't defined

Fixes #5627: Added `yii cache/flush-schema` console command to flush DB schema cache of a given database connection