[Nitro] user registration / authentication: email validation

[Martin Bernd Schmeil]

Hi Ysabel, hi Michael,

thanks a lot for taking care about this auth-stuff. As I said I don't 
feel experienced enough
to write good Ruby code and I don't know about the nitro-auth design. 
I'm looking for
something that works like the mechanism that Michael described.

I might do the task if noone else moves first. But that can take some 
time...

Thanks! - Bernd