Cleanup of Filenaming

[colinbjohnson]

Currentle exported filenames are written by converting last, first and filename - particular filenames with characters outside of ascii range are not able to be encoded. The lines used to avoid this problem are a hack:

try:
    file_name = '{!s}-{!s}-{!s}'.format(last, first, attachment.file_name)
except UnicodeEncodeError:
    logging.warn('Failed to encode filename for: {!s}'.format(attachment_id))
    continue