Fixing the issue #3292

This change fixes the issue #3292. The details were mentioned in the comments to the issue.
Update DefaultValueValidator.php

Allow the default value to be a closure
Update CHANGELOG.md
Update DefaultValueValidator.php
Update config.php
BaseVarDumper::export() added
Doc comments for `BaseVarDumper::export()` added
Issue #3232 added to CHANGELOG
Object handling at `BaseVarDumper::export()` reworked
Check if property is set

```getValue``` didn't check if the property on an object exists so wouldn't return the default value.
add Korean Language Translation
Update yii.php
Update config.php

add "ko" value for languages array
Advanced app's common tests codeception generated files gitignored
Tests excess dump removed
improved debugger on handling unreadable files

issue #3494
guide WIP
added note about GET method to ActiveForm

fixes #3353
Merge pull request #3496 from LAV45/fix

Tests excess dump removed
fixed broken link