Update gii.md

fixes for https://github.com/yiisoft/yii2/issues/951#issuecomment-25934549
upd image
Hide debug toolbar when media = print

fix https://github.com/yiisoft/yii2/issues/3050
Update model.md

Add `whenClient` description
Update model.md
Merge pull request #3105 from githubjeka/patch-4

Update model.md
Merge pull request #3103 from githubjeka/patch-3

Hide debug toolbar when media = print
Updated changelog
Merge pull request #3102 from githubjeka/origin/patch-2

Update gii guide.