API CHANGE: Added a ticket mime type method to the ticket generator interface.
API CHANGE: Added a ticket mime type method to the ticket generator interface.

silverstripe-australia/silverstripe-eventmanagement,souldigital/silverstripe-eventmanagement,burnbright/silverstripe-eventmanagement,registripe/registripe-core,souldigital/silverstripe-eventmanagement,silverstripe-australia/silverstripe-eventmanagement,stephenmcm/silverstripe-eventmanagement,burnbright/silverstripe-eventmanagement,stephenmcm/silverstripe-eventmanagement