Improved `QueryBuilder::buildLimit()` to support big numbers

Revert "Fixes #1856: The default CSS class for hint generated by `ActiveField` is changed to `help-block`"

This reverts commit 7ae4695d.

Fixes #2212: `yii\gridview\DataColumn` generates incorrect labels when used with nosql DB and there is no data

Fixes #706: Added `yii\widgets\Pjax` and enhanced `GridView` to work with `Pjax` to support AJAX-update

fixes #1842

fixes #2196

realpath(false) = current working directory.
This can cause problems with getAlias() which returns false.

see yiisoft/yii#3113

fixes yiisoft/yii#2844

which resulted in endless loop

http://www.yiiframework.com/forum/index.php/topic/50982-cfilehelper-bug-security-flaw/

Added `yii\web\Request::get($name = null, $defaultValue = null)` and `yii\web\Request::post($name = null, $defaultValue = null)`

CS fix.