Fixes #1897

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

Merge branch '2048-improve-messages-config-exceptions' of github.com:nineinchnick/yii2 into nineinchnick-2048-improve-messages-config-exceptions

Conflicts:
	framework/messages/config.php

Merge branch 'request-params-refactoring' of github.com:cebe/yii2 into cebe-request-params-refactoring

Conflicts:
	framework/CHANGELOG.md

fix

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

Conflicts:
	framework/CHANGELOG.md

Codeception ext docs fix

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

* 'detail-view-attributes' of https://github.com/creocoder/yii2:
  DetailView phpDoc
  CHANGELOG
  DetailView allow set label while attribute in string format
  DetailView correct regexp

Conflicts:
	framework/CHANGELOG.md

i18n docs added

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