Replace "Marketplace" with "Dealers Room"

AC wanted to remove all references to the Marketplace, since it doesn't
exist.
Change under 13 message

Alters the under 13 message to fit AC's preferred tone. Still uses the
age_group_desc so it can still work for other events.
Limit printed badge name

Limits the printed badge name to 20 characters, so badges can actually
be printed correctly.
Stripe form customization

Enables zip-code verification on the stripe form, and replaces the
MAGFest logo with the AnthroCon logo.
Merge pull request #699 from magfest/text_changes

Last-minute text changes