Add linkflair classes to body

This will allow styling comments pages differently depending on the
linkflair of the submission.
modaction: Allow querying by multiple moderators.
modaction: Add filter by admins.
subreddit traffic: Link to subreddit search by time period.

Traffic spikes on the subreddit traffic pages are currently very opaque.
There's no simple way to determine what could have caused a big change.

This makes the date/time column of subreddit traffic tables link to
timestamp-limited subreddit search for that subreddit.  While this
doesn't cover external referrers etc. it should give some insight into
traffic.
log_q: Add SystemExit to the ignore list.

This is what will happen if gunicorn receives a SIGTERM (indicating
non-graceful worker shutdown -- likely because the worker has overstayed
its welcome) and so it's not actually useful information.