fixes #1905

fixes #2094

Fixes #2016: removed ability to declare scopes in ActiveRecord leaving it to ActiveQuery. Changed documentation accordingly.

https://github.com/yiisoft/yii2/blob/master/extensions/redis/Cache.php#L16

Text amended as "A new method" was referring to two. CHanged the text to "New methods".

Correction name ru_RU zh_CN to ru-RU zh-CN

Updated extension docs to be less restrictive about choosing namespace, more neutral composer.json example

Make clear that "type" in extensions' namespaces must be in plural form (widgets/behaviors/modules)