Fixes #2204
For Imagine v0.5 (previous code was for 0.6 dev)
Fixed the fact that there's SafeValidator
Allow multilevel dropdown.
Locked Codeception versions since master is under heavy refactoring
#2248: Renamed `yii\base\Model::DEFAULT_SCENARIO` to `yii\base\Model::SCENARIO_DEFAULT`
Added array initialization
Added array initialization
Removed unnecessary variable
Removed unused variable
Fixed minor coding style issues
More consistent usage of MessageFormatter::tokenizePattern
Revert "Locked Codeception versions since master is under heavy refactoring"

This reverts commit 7145b9e9a7da9eddfbdc0d7dc6e7eea2a9051371.
Fixes #1412: `FileValidator` still triggers `uploadRequired` error in some case when `skipOnEmpty` is true and no upload is provided
Merge branch 'master' of git://github.com/yiisoft/yii2
Merge pull request #2229 from klevron/2204

Fixes #2204
fixed test break.
fixed dev config.
Refactored debug module, added all missing docs
Minor cleanup for debug module