Configuration of required attributes for registration

[tkrille]

At this time one can only configure what fields show up on the registration page. Which fields are required or not is statically implemented and so cannot be changed by a deployer/operator. I think we should make it possible for a deployer/operator to define which fields are required or not. @dacrome already made up an example how to specify that in the properties file: https://gist.github.com/dacrome/31edbb3b9e894258e937

[dacrome]

I think we need a custom validator to handle all fields of the user

[dacrome]

@tkrille which fields are required is changeable by deployer/operator via the templates, by just setting the last parameter to true/false. But for sure it is way easier to do this by configuration. I think this is a low hanging fruit, because everything is prepared to fulfill this feature.