Mass mailer should only include valid tickets

[malemburg]

The mass mail interface for attendees currently returns all tickets assigned to the user, including canceled ones (frozen status), and ones for which the payment process was not completed.

The correct query for tickets would be:

# Get all valid conference tickets (frozen ones are not valid)
tickets = cmodels.Ticket.objects.filter(
    fare__conference=conference,
    fare__ticket_type='conference',
    orderitem__order___complete=True,
    frozen=False,
    )