part 1 of notif refactor
added filterUids method to privileges

used to filter uids on a single category
check err
less db calls
removed derp
removed total count
closes #2074

when new notifications are pushed to uids clear their old notifications.
faster notif prune

no need to loop tru and check datetime since notifications is a sorted
set now
notification fixes

made post notifications unique per post so they dont overwrite other
types.
added topic titles to notifs

upvote, favourite and flag has topic titles now
cleanup
pagination fix