New feature: Form Validation

cf: https://github.com/Evaneos/ev-fdm-demo/pull/5

![https://lh3.googleusercontent.com/-vbW7A8jkPvo/VHbPN_wjpUI/AAAAAAAADrs/m--EIuKyj80/w324-h191-no/abd-215.gif](https://lh3.googleusercontent.com/-vbW7A8jkPvo/VHbPN_wjpUI/AAAAAAAADrs/m--EIuKyj80/w324-h191-no/abd-215.gif)