Displays per-camp fields to authenticated users.

Updates applicant info function to return both application info and user data.

Instead of returning either applicant_info or user data, the
thatcamp_registrations_get_applicant_info function returns an object
containing data from both the applicant_info and existing user data. This
helps with displaying values from both for when authenticated users fill out
the registration form.

Fixes #63.

(Note that most of the changes in `thatcamp-registrations-public-registration.php` are indentation clean up/consistency. had to do this to make sure I added my code in the right places.