fix the validation of the form in demo/tab.html and add some required messages in order to validate the demo/date.html.

about the demo/tab.html, i fixed the validation of the form, so as you can see here is a picture before and another after fixing the problem
Before:
![before](https://cloud.githubusercontent.com/assets/6888059/3757443/29061f5c-1839-11e4-9dfc-6da32878477b.png)

After:
![after](https://cloud.githubusercontent.com/assets/6888059/3757447/318ba41c-1839-11e4-8725-796639b887cd.png)

and also, i added some required message in order to validate the form in demo/date.html