* Add ability to mark dmails as unread.
* Fix users.unread_dmail_count to not count deleted dmails.
* Fix show action so that API calls don't mark dmails as read.
* Don't show the unread dmail notice on the /dmails page itself.
* Stop using users.has_mail flag.
* Add unread and deleted dmail folders.
* Remove dmail_folder cookie (wasn't used).
* Default to the received folder so that we don't show sent messages by default.
Turn deletions into soft deletions (set the is_deleted flag) instead of
hard deletions (remove from database). The is_deleted flag actually
already existed, but it was never used before.
Few people used dmail filters (~900 users in 5 years) and even fewer
used them correctly. Most people used them to try to block dmail spam,
but usually they either blocked too much (by adding common words that
are present in nearly all dmails, causing all mails to them to be
filtered) or too little (blocking specific email addresses or urls,
which usually are never seen again after the spammer is banned).
Nowadays the spam detection system does a better job of filtering spam.
Change calling convention to explicitly indicate whether the attributes
are for the <th> element or the <td> element. Fixes various cases where
the two were mixed up.
* Fix .col-expand classes not being set correctly on the /post_versions,
/pool_versions, and /notes pages.
* Fix .updater and .updated-at classes not being set correctly on the
/forum_topics page.
* Fix the name param being ignored (noticeable in the post count field
on the /tags page).
* Don't pass empty string when column has no name.
