Update registration_period update function so that it is less noisy
Add gender-breakdown to the events#summary registrants counters. Add country+gender to the Edit All Registrants page
update the payment#summary num_unpaid column to hide deleted registrants' info
add age to the registrants#index_all page
don't accidentally add-back the registration item if refunding a non-registration-item
allow administrators to create/delete registrant_expense_items, and to see the #items page for all registrants