Merge pull request #4995 from mikehaertl/master

[ci skip] Update docs for CheckboxColumn::$checkboxOptions
reverted a previous change .
Additional fixes
Merge pull request #4998 from creocoder/aliases-to-bootstrap

Additional fixes for #4993
Typo in concept-behaviors.md

The method 'bar()' does not exist in this context. I believe it should be 'foo().'
Merge pull request #5002 from willaustin/patch-1

Typo in concept-behaviors.md
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
Added polish guide
Added polish guide
Fixes #4938: When `yii\db\ActiveQuery` is used to build sub-queries, its WHERE clause is not correctly generated
Update structure-views.md

Above/below code reference fix
Merge pull request #5009 from tebazil/patch-1

Update structure-views.md
Complete translation of `input-validation.md`
Edited Russian translation of Behaviors
Fixed errata
Edited Russian translation of Components guide
Edited Russian translation of Configurations guide
Edited Russian translation of Properties guide
Edited Russian translation of Service Locator guide
Fix Typo for concept-aliases