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

Enh #4424: Added `forceDownload` parameter to `yii\web\Response::xSendFile()`

Enh #3459 : Added logging of errors, which may occur at `yii\caching\FileCache::gc()`

`yii\base\ErrorHandler::handleError()` adjusted keeping native error processing on error reporting miss match.

Docs Rissian translation: translated rest-versioning.md [skip ci]

Codeception test adjustments for basic and advanced applications

RFC 7232 Compliance for yii\filters\HttpCache