Adding CORS filter to allow Cross origin resource Sharing
Adding enhancement CORS
Move methods
Fix changelog
Merge branch 'master' into feature/CORS
Allow the user to override the request like in RateLimiter
Fix multiple headers management in Access-Control-Request-Headers
Allow the user to remove field by nulling it's value. Usefull for Access-Control-Max-Age
Remove static functions
Fix unused var
Fixes #3443: Fixed `yii\bootstrap\Nav` and `yii\bootstrap\Dropdown` were generating wrong ids for submenus
Merge pull request #4193 from pgaultier/feature/CORS

CORS Filter
Russian translation - semantic fix [skip_ci]

Example

```
['profit', 'number', 'min' => 0.01],
```

Value 0.01 is allowed
Check for UPLOAD_ERR_NO_FILE in UploadedFile

fixes #4276, close #4358
Merge pull request #4364 from SDKiller/patch-5

Russian translation - semantic fix [skip_ci]
`yii\web\Request::cookieValidationKey` is now automatically generated by the installation script for the basic and advanced application templates
Request::cookieValidationKey must be explicitly specified now.
Fixes #4048: Added `init` event to `ActiveQuery` classes
Refactored code.
dropDownList encodeSpaces for subgroups

fixes #4105, close #4376