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
Add $key to function parameter

I think it's better to enclose `$key` as function parameter.
Fixes #3548: Fixed the bug that X-Rate-Limit-Remaining header is always zero when using RateLimiter
Merge pull request #3546 from mikehaertl/master

Issue #3532: Add note about AR default values to upgrade notes
Improve `in` validator to properly support array attributes.
Fixed test break of Html.
Merge branch 'master' of git://github.com/yiisoft/yii2
Update CHANGELOG.md
Fixed allowance for ratelimiter. [skip ci]
Log for pull request #3544
Added CodeClimate quality score