(bug 4772) show users using standard userhead

Also, use load_userids to pull users from the database as a group,
instead of loading them one by one with calls to LJ::load_user.

Previous branch: bug4772-stats-old-urls; previous pull req:
https://github.com/dreamwidth/dw-free/pull/337
(bug 4772) Style cleanup: remove trailing parens()
(bug 4772) use more idiomatic "if ( @$accounts )"

Address Fu's comment here:
https://github.com/dreamwidth/dw-free/pull/337#discussion_r3792867

Alter this from "if (scalar @$accounts == 0)" (if there are
no accounts in the results, do this, else process them)
to the (hopefully) more readable "if ( @$accounts )"
(if there are accounts, process them, else display an error message).
(bug 4772) rework code that creates <li>s

Each element of @$accounts is a hashref like so:
 { userid => 1234 , timeupdate => '2013-03-30 01:58:32' }

Then LJ::load_userids gives us a hash that lets us map userid numbers
to user objects.  Unfortunately, we need to keep the @$accounts array
around to preserve the ordering -- they're sorted by last update time.

Hopefully subbing in the conventional $u will make what is going
on here clearer.  If not, we'll have to rework this in a more
readable but less efficient way. ^_^;

Addresses afuna's comment:
https://github.com/dreamwidth/dw-free/pull/337#discussion_r3792930