Proposal for #827 Add ImageValidator

Little explanation on the IP whitelisting

I wasted >1h trying to find out why the debug bar was not shown on my remote staging server. Hopefully this will help other people avoid this mistake...

Fixes #1133: gii controller generator now uses application controllerNamespace as default value for "Controller Namespace"

* 'master' of github.com:yiisoft/yii2:
  doc fix
  Fixes #1134: doc fix.

- refactored replaceNamedArguments.
- ensure gridview message works on all systems.

fixes #1072

fixes #1131

fixes #1132

* 'master' of github.com:yiisoft/yii2:
  Fixes #1115: fixed the issue with PDO boolean value binding with pgsql

Typo in Docs [skip ci]