Limit email address length

An excessively long email address will cause Stripe to fail during
checkout, so users are now limited to 255 characters.
Fix birthdate error

Fixes the check for date of birth so that it actually triggers now.
Improves error for invalid age group.

If age groups haven't been added to the database, the attendee's age
group is set to None, which causes 500 errors. Prevents these errors by
displaying a more user-friendly error message.
Merge pull request #643 from magfest/fix_age_group_None_error

Improves error for invalid age group.
Merge pull request #641 from magfest/fix_stripe_email_error

Fix stripe email error
Adds volunteer config option

This is a temporary solution for AnthroCon, so it's just a simple config
option to hide the volunteer checkbox.
Merge pull request #646 from magfest/remove_volunteer_checkbox

Adds volunteer config option
fix for broken prereg form
Revert "Improves error for invalid age group."
Merge pull request #648 from magfest/revert-643-fix_age_group_None_error

Revert "Improves error for invalid age group."
Removes default parameter to fix dealer reg

For some reason, defining the default badge type broke dealer
registration. This replaces that with a check to see if the badge type
is set.
Add Emergency Contact name

Adds a field to the preregistration page that requires attendees to
enter the name of their emergency contact. This is not required if
they're international.
Add EC name to registration forms

Adds the emergency contact name to the admin and at-door registration
forms.
Merge pull request #653 from magfest/add_ec_name

Add Emergency Contact Name
Merge pull request #650 from magfest/fix_dealer_reg

Removes default parameter to fix dealer reg