added tabs
add fixes
\yii\jui\Widget::registerWidget() improvement
jQuery UI sortable widget
Refactoring
Comment fix
theme => enableTheme
enableTheme => registerTheme
Introducing items
Merge branch 'master' of https://github.com/yiisoft/yii2 into jui-sortable
Error/exception page is now 100% fluid.
Update Cache.php

Fixed an example of using buildKey in the doc
Fixed stack trace bug and added class/method call information.
Previous exceptions refinements.
Proper colors.
Method "AssetController::adjustCssUrl()" has been created as blank
Fixed typo in ErrorHandler

`$this` -> `$self`
Sortable rework
jQuery UI accordion rework
More refactoring