minor doc fixes
Fixes #1941 reset CHtml:: instad of hardcoded value
send CHtml::errorCss to JS file
added changelog
Merge pull request #1944 from mdomba/1941-CACtiveForm-reset-errorCss

Fixes #1941 cActiveForm form reset
[ci skip]
Fixes #1942 CActiveForm client validation
Merge pull request #1946 from mdomba/1942-CActiveForm-clientvalidation

Fixes #1942 CActiveForm client validation
[ci skip]
Improved docs for CArrayDataProvider::$keyField

Issue #1943
added `@todo` comments to gii model template

Fixes #1951
Throw exception on missing PDO class in CDbConnection

issue #645
updated german translation files
updated copyright year in docs
ru: fixed broken link in the guide
Merge branch 'master' of git://github.com/yiisoft/yii into uk-docs