Using required a11y attributes for forms (bug 765147)

![capture d ecran 2014-08-13 a 10 58 36](https://cloud.githubusercontent.com/assets/3556/3903349/d998f128-22ca-11e4-80e5-7eae1f165649.png)
![capture decran 2014-08-13 a 10 59 38](https://cloud.githubusercontent.com/assets/3556/3903352/df7921e4-22ca-11e4-9eb1-6c26b8b94725.png)
![capture d ecran 2014-08-13 a 10 59 49](https://cloud.githubusercontent.com/assets/3556/3903354/e192be68-22ca-11e4-9a46-507cac3c8917.png)

Maybe a RequiredInputMixin at this point?