Added EventTicket::getAvailableForDateTime() to return how many tickets are available for a specific event time.
Added EventTicket::getAvailableForDateTime() to return how many tickets are available for a specific event time.

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