asArray will not include null valued keys

fixes #1311

Fixes #5126

- in composer the `~` operator is just a shortcut for `~1.0` = `>=1.0.0,<2.0.0`
  it does not prevent dev versions to be installed but neither does `1.*`
- dev versions are constrolled via `minimum-stability` setting and the
  `@dev`, `@beta`, `@stable`,... settings.
- setting bower packages that ship compiled files only with the stable
  release to use `@stable` in composer.json of the applictaions. This
  setting can be removed when we remove the `minimum-stability=dev`
  setting after GA.

fixes #5104, fixes #5101

Fixes #5058: `yii\helpers\Html::activeCheckbox()` and `activeRadio()` will generate labels by default using the corresponding attribute labels

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

close #4487

close #4505

fixes #4452, close #4452