Added 'caseless' option to `yii\helpers\BaseFileHelper::findFiles()`
Convert 'caseless' option into 'caseSensitive' option at `yii\helpers\BaseFileHelper::findFiles()`
Merge pull request #4752 from klimov-paul/4062-find-files-case-sensative

Enh #4062 : Added 'caseless' option to `yii\helpers\BaseFileHelper::findFiles()`