delete observ obj when observed obj is deleted
auto delete observations & sender_to_link bug
add tool tip to checkboxes
notice_unseen tag & sent[] on send

-send_observation_notices_for now returns a list of recipients so that
additional calls can add it to exclude.
-notice_unseen  template tag:  allows easy css switch for notice
indicator. 0 = 'none' >0='unseen'