Add support to Eventbrite

[tonyhhyip]

Reason: For use in Hong Kong

Feature to add:

• Allow attendee to scan Eventbrite ticket barcode in the app
• Add endpoint for Eventbrite webhook for capture attendee purchase ticket and check in events (https://www.eventbrite.com/platform/docs/webhooks)

[tonyhhyip]

cc @denny0223

[tonyhhyip]

Allow attendee to scan Eventbrite ticket barcode in the app is solved by generate token method

[tonyhhyip]

More detail:

attendee purchase ticket and attendee update webhook:
Usage: adding attendee to database by programme after they buy the ticket or update their information

Attendee check-in webhook:
Usage: record attendee check-in in server
Reason: we can still make us of Eventbrite app without having a static placed computer for manual check-in and we have some crazy problem on having someone forcing us to use a strange label printer