close #2543

Fixes #2392: Added `addCssStyle()`, `removeCssStyle()`, `cssStyleFromArray()` and `cssStyleToArray()` to `Html`

fixes #2519: MessageSource removed translation messages when event handler
was bound to `missingTranslation`-event

allow extending only one class to add scopes, fixes #2146

TODO:

- [ ] adjust guide docs
- [ ] adjust README files of extensions
- [ ] finish work and fix test breaks

Fixes #2360: Added `AttributeBehavior` and `BlameableBehavior`, and renamed `AutoTimestamp` to `TimestampBehavior`

fixes #2265

Fixes #1186: Changed `Sort` to use comma to separate multiple sort fields and use negative sign to indicate descending sort

better not delete all to avoid data loss

pr #2324

```
$result = Article::find()->query(["field" => ["title" => "yii"]])->all();
````

- DbMessageSource now performs UNION ALL.
- Fixed message merging for php and po.
- Updated tests.

Comment test because it proceed an errors when tries to run at mssql and other DBMS.