Fixes #5039: `UniqueValidator` and `ExistValidator` did not respect query conditions added by default scope

[skip ci] Added polish guide - README.md

Conflicts:
	framework/console/controllers/HelpController.php

Chinese Translation for last month

[skip ci] ncessary -> necessary

Translate guide/start-gii into pt-BR

Hello,

I used **Yii2 authclient** to build a Github OAuth (2.0) client, and performed a POST call to create a Github repository hook. But I got this exception:

```
exception 'yii\authclient\InvalidResponseException' with message '
Request failed with code: 201, message:
{
	"url": "https://api.github.com/repos/ychongsaytc/example/hooks/1000000",
	"test_url": "https://api.github.com/repos/ychongsaytc/example/hooks/1000000/test",
	"id": 1000000,
	"name": "web",
	"active": true,
	"events": ["push"],
	"config": {
		"url": "https://example.com/payload",
		"content_type": "form",
		"secret": null
	},
	"last_response": {
		"code": null,
		"status": "unused",
		"message": null
	},
	"updated_at": "2014-09-14T03:02:55Z",
	"created_at": "2014-09-14T03:02:55Z"
}
' in /home/ubuntu/public_html/live/vendor/yiisoft/yii2-authclient/BaseOAuth.php:206
```

I think a successful API call is not always exactly return **200** status, like **Create a hook** API of Github: https://developer.github.com/v3/repos/hooks/

It will return `201 Created` if hook was successfully created.

In my opinion, is status code starts with **20** in normal scenario?

close #5011

Update structure-views.md

Above/below code reference fix

Fixes #4938: When `yii\db\ActiveQuery` is used to build sub-queries, its WHERE clause is not correctly generated

Fixes #5001: `yii\rest\CreateAction`, `yii\rest\UpdateAction` and `yii\rest\DeleteAction` should throw 500 error if the model operation returns false without validation errors

Typo in concept-behaviors.md