RSVP: Add shirts to last page

Add shirt choice in the RSVP flow. This requires
another Paypal item code.
Shirts: Add 2014 designs

Update the image files to reflect the 2014 design
by Laurel Thompson.
RSVP: Modify shirt txt in email

Now that shirt ordering is part of the RSVP process,
the language in the email should be slightly different.