separate log and backlog tables
Currently only backlog table exists.
Having a separate log table would leave more freedom in having an entry logged, but not displayed in the channel/users tree.
Once a channel or query is "closed", its backlog is deleted while it is only retained in logs.
Once a channel or query is activated, its logs are moved to backlog.
(There are hundreds of entries which are only activated few times a year, or just once at all, and keeping them in backlog is useless.)