Refactored AR find
Fixes #3016.
Added `isAssociative()` and `isIndexed()` to `yii\helpers\ArrayHelper`
Finished refactoring find() .
Merge branch 'master' into split-find-into-find-findOne-findAll
updated change log.
Merge pull request #3003 from yiisoft/split-find-into-find-findOne-findAll

Refactored AR find to fix #2999
Wrong placeholder in translation
auth guide fix
changelog fix.
Merge pull request #3021 from zelenin/auth-guide-fix

Authorization auth guide fix
Use proper error message.
Merge pull request #3019 from ufisch/master

Wrong placeholder in translation
Better executeRule implementation.
Fixes #2968.
Merge branch 'master' of git://github.com/yiisoft/yii2