Issue: Broken Read Marking Adds Queries

Currently read marking doesn't really work. It adds a marker only when viewing a discussion thread or a page that has one below, and does so on every page. Additionally, it only works for logged in users and only if database marking is turned on.

Fixed. Read marking now works for both registered users and guests, and falls back to the cookie if none is found in the database. Also, removed the query in most cases by only updating the marker if the page's last update is more recent than the last read time.