Redesigned registration views to just pass cleaned form data to the registration profile for processing

This redesign separates the registration view of concerns about which fields a registration profile needs to create users. It now simply passes the validated and cleaned form data to the ````create_inactive_user```` method of the registration profiles manager. The registration profile manager can then use any fields contained in the clean data to create an inactive user. This also allows the ````create_inactive_user```` method to have a consistent signature for any registration profile, since the user data is just passed through.