When the capaicty is 0 display the modal link and support when JS is disabled.

#5051

![generic](https://f.cloud.github.com/assets/1222368/2125662/5cbc6e24-9255-11e3-922c-d5f42d2e201c.png)
![selection_011](https://f.cloud.github.com/assets/1222368/2125663/5cdbf712-9255-11e3-9467-2b73337b8e95.png)

I changed the location of the default email field and also added a validation function for the new mail. This PR also fix the capacity limit: when it's 0 the registration is unlimited and when not the limitation will be validated and checked the event is fully booked when the user will try to register. I also fix the modal link when the JS is disabled. This will help us when the behat testing are running.