fixes#12840
Used @nkovacs draft as starting
point(https://github.com/yiisoft/yii2/issues/11037#issuecomment-193356450).
I also fixed some bugs in `yii.validation.js` and did some refactoring.
Implemented tests:
- yii.validation.js
Running tests:
- Install Node.js. I used the latest version available at the moment -
`v7.1.0`. Note that used `jsdom` dependent library version requires
`Node.js >= 4`.
- Run `npm install` to install dependencies.
- Execute `npm test` for running tests.
