Refactored code.
dropDownList encodeSpaces for subgroups

fixes #4105, close #4376
Added support for relation by array attributes

fixes #1249
added elasticsearch test case for array attribute relations
fixed issue with indexBy and array valued relations
Fixes #3611: Refactored query caching.
typo fix [skip ci]
Sphinx distributed indexes support provided
Fixes #4384.
Update ActiveRecordInterface.php

fixes #3026
Update .travis.yml

temporarily skip app tests as they seem to be broken somehow
#4310: Removed `$data` from signature of `yii\rbac\ManagerInterface`
Fixed test break.
#4388: CORS filter fixes:

- Upgrade the documentation to match filter code
- Fix bad default behavior with Access-Control-Allow-Credentials
- Fix missing "s" in header Access-Control-Request-Method / Access-Control-Allow-Methods
Better fix for Dropdown container options

Better fix for #3443 that does not break BC and allows widget to be extensible.
Merge pull request #4393 from kartik-v/patch-1

Better fix for Dropdown container options
Doc translate for rest-resources
Merge pull request #4394 from MikeBazhenov/master

Doc translate for rest-resources
minor refactoring of FileValidator.
Fixes #3887