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
Check if property is set

```getValue``` didn't check if the property on an object exists so wouldn't return the default value.
Method to unlink all relationship many to many in current model
add change to CHANGELOG,and mini refactoring
add #3520 to changelog
change nik name (case sensitive)
Add support all type relation
Adding rotateByCopy to yii\log\FileTarget #3562
Merge pull request #3585 from pawzar/dev

Adding rotateByCopy to yii\log\FileTarget #3562
added test case to acually create cols with virtual type

verify issue #3473
Docs about cross-DBMS relations added
Example code consistency fix
Incorrect path to AppAssets at docs fixed
Merge pull request #3588 from klimov-paul/3429-docs-app-asset-location

Fix #3429: Incorrect path to AppAssets at docs
Fix 'db-active-record.md'
Merge pull request #3586 from klimov-paul/2020-doc-cross-dbms-relations

Fix for #2020: docs about cross-DBMS relations
Fix incomplete obsolete filling in i18n db extractor

Obsolete keys searching isn't work when we have serveral categories for tranlation with DbMessageSource. Obsolete array filled with last message category only, because it'll always overwritten.