New truncate and truncateWords methods

New truncate and truncateWords methods, https://github.com/yiisoft/yii2/issues/2941
Update BaseStringHelper.php

Length check.
Update CHANGELOG.md
Update BaseStringHelper.php

Updated to use mb_* functions
Test case for new truncate methods.

Test case for new truncate methods.
Update BaseStringHelper.php
Issue #3154 - DataColumn filter model validation error indication added
Issue #3154 - GridView - list of filter model validation errors added to summary
Issue #3154 - DataColumn checkForFilterErrors() now use Html::addCssClass
Fix the Y2K38 bug

Adds support for timestamps beyond year 2038.
Update CHANGELOG.md
Merge pull request #3194 from kartik-v/patch-16

Fix the Y2K38 bug
Fixed test break.
Fixed code block formatting
Update CHANGELOG.md

Moved line and added author. Fixes #3198
Fixes #3204: `yii\di\Container` did not handle the `$config` parameter well in case when it does not have a default value
Fixes #3208
Fixes #2853: ActiveRecord did not handle resource-typed columns well
Update BaseStringHelper.php
Changelog update