indexes were missing on foreign keys for "message", "subject" and "thread" tables, seriously impacting performances.
In addition to those indexes, two indexes have been added to speed ordering by timestamp on "history", and one on "files" table.
history.rowid is not used anymore as there is an index on (profile_id, received_timestamp) which will speed up the query.
Primary keys order has been changed to use automatic index in most common cases (filtering by profile_id then namespace).
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