Feature/i18n for ticket system

Identity.new.valid? should not crash. So validate presence where needed and
skip the other validations if the value is absent.

errors.each iterates through all errors for all attrbibutes nicely.

We create an identity alongside each user. Make sure the identity
is valid when creating the user. This also ensures that the login
picked is available because otherwise the identities address would
not be available anymore.

This will print missing translation keys at the end of the tests

hash token with sha512 against timing attacs #3398