Payments: Use Paypal item numbers

... not the button IDs.
Payments: Return to our site after payment
RSVP: Put proper payment amount in email

... if a shirt is ordered.
Errors: Check res.headersSent

... not res.headerSent
Payments: Always log Paypal notifications

... that match the items we care about, anyway.
Payments: Add routes for auto redirect
Payments: Fix reference error