Change the way email validation is skipped.

Email validation is now not simply skipped during non-production mode.
The reason for this is that we actually want to test sending of emails.
Instead, one can call #skip_email_validation! on a user object before
saving it.
Testing email confirmation.

We now require users to verify their emails before utilizing the system
and the tests obviously need to reflect this. This adds test coverage
for email confirmation.