Move website from User to UserProfile

This is a first part of changes requested in https://meta.discourse.org/t/a-small-ruby-db-refactoring-task/16042: `website` is moved from User model to UserProfile model. 

Let me know if you have any feedback.
It should be possible to just call  `user_profile.website` if all users have a profile
https://github.com/abezzub/discourse/blob/website/app/models/user.rb#L78