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.

hash token with sha512 against timing attacs #3398

Email.new(nil) now returns an invalid email rather than crashing.

use the former if you want a working email account or nil, the
latter if you want the email address associated with a given
user no matter if the user actually has an email account or not.

The changes to the configuration required some non minor changes to the platform and also added some flexibility we don't require yet - and thus some new possibilities for errors.

So instead we still use the allow_..._certs and ..._cert_prefix options.
They basically provide the framework in which service levels can operate.

The service level configuration will not include the cert prefix anymore.
It only states if the service level is rate limited or not.
This avoids conflicts between the two configuration options.

I also removed the anonymous service level entirely.
It was also turning a boolean decision (do we provide anonymous eip or not) into something way more complex. Instead I added the AnonymousServiceLevel class to handle the corner cases for people who are not logged in.

Furthermore i renamed the UnauthenticatedUser to AnonymousUser so it matches the Anonymous Service Level nicely. It's also shorter and more intuitive.

cleaned up all the engine stuff that was never really used.
Afterwards there is not that much left that makes it into the toplevel.