Refactored signup and password fields

Added more resources for user signup strings
AjaxPassWordView now accepts an external additionalError, this is
provided to validate password, or check repeat matches etc.
Added email validation to User object.
Refactored errors in UserSignup, can use the same Cals for errors in
AjaxTextViews and also when notifying user that they cannot signup yet,
for enable/disable of button, and for validation before actually
keeping the user in mongodb.