- Gii diff markup is now copy paste friendly
- Removed StringHelper::diff()
- Moved phpspec/php-diff dependency from yiisoft/yii2 to yiisoft/yii2-gii

Fixes #2157: The '*' category pattern will match all categories that do not match any other patterns listed in `I18N::translations`

Allow writing widgets using return instead of echo in the run method to make it consistent with controller

fixes #2132, fixes #2133