Pull in tickets via Eventbrite API

[cjwhitsitt]

Some events use Eventbrite for ticket sales. Instead of making a static list of tickets, pull in the ticket types, cost, and availability from the Eventbrite API if creds are given via the admin panel.

Some events use Eventbrite ticket types for things like sponsorship which you may not want to show in the ticket list on the website. To solve this, maybe include a checkbox to hide certain ticket types.

[MrCsabaToth]

Eventbrite ticket and coupon system itself allows to make some tickets hidden, or make some coupons visible by default. I expect that those should come through the API.

[MrCsabaToth]

Given that this would use admin level (although read-only if possible) Eventbrite API, this would be an optional part of the build process? We need to figure this out more for a clearer specification.