Fixes #13. Implement DB message source.
Added Jsonable support.
Merge branch 'master' of github.com:yiisoft/yii2
Minor refactoring of t().
Merge pull request #512 from resurtm/DbMessageSource

Fixes #13. Implement DB message source.
Response WIP
Merge branch 'master' of github.com:yiisoft/yii2
Minor refactoring of DbMessageSource.
CS fixes.