See badge_num NULLABLE to true

Sets the badge_num column to be nullabe to match the live schema.
Fix 500 error when calculating group price

The attempt to add an age_discount to a whole group caused uber to fail
catastrophically. Removed that line.
Fix Stripe Error

Stripe payment for groups was failing because it was trying to get an
email that doesn't exist. Added a check for email variable to prevent
the error.
Merge pull request #761 from magfest/fix_group_errors

Fix group errors