Admin: Provide error check/validation mode for room bookings

[ottlinger]

An additional admin view (selectable by week) should show any names with double bookings. db_booking_errors.php

If these lists contain any elements this indicates errors in the booking process that should be fixed!

(e.g.

• [x] people with bookings in both weeks
• [x] people with double bookings in one week (same person blocks more than one room) -> same as before
• [x] any rooms with more bookings than capacity
• [x] allow jumping to an applicant with errors -> db_applicant.php )