Ndupoux/fixing registration page

I've edited the user registration page in order to prevent new users from using their password as their public username. 
With the current registration page layout, many users erroneously set their password as their public username, since the username field is directly below the password field. 
To fix this issue, the existing username and real name form fields have been moved above the password field and a password confirmation field has been added. Two simple validations have been added to the create_account handler to make sure that the password and password confirmation fields match and that the password field and username fields do not match when a user submits the registration form. I've also edited existing tests to now incorporate the added password confirmation field. 
@jrbl @jinpa @sarina 



What happens in the case where
```
username = foobar
password = foobar
password_confirmation = blabbity_blah
```
Clearly the cases you have show that it will error, but what's the precedence? Which error is it?