Add "Who helped you with your purchase?" text field to customer info page

[griebelr]

• [x] Add new text field on the customer information page of adventurepass.us (public paid site)
• [x] Field name "Who helped you with your purchase?"
• [x] Field is not required
• [x] Field placement is below RV Owner and RV Type, above Next button
• [x] Save typed answer in db and index for reporting