Logging last session start / last activity

I've re-implemented the red (new posts) / yellow (no new posts) folder behaviour.

If you're technically included here's how it works:

For logged in users

When you login we'll store the login time in user_last_session_start. As you view pages we'll store the last page view time in user_last_visit

When viewing the site index or a topic index we'll compare the user_last_session_start against the last_post_time. If the user_last_login is before the last_post_time the folder icon will be red (new posts). This behaviour will persist for the whole session ie viewing a topic won't turn the icon yellow.

Then let's say you don't visit Tiki Central for a few days.

When you next visit Tiki Central we compare the user_last_visit with the current time. If user_last_visit is more than 2hrs ago we use that as the new user_last_session_start. This will then show all new posts since user_last_visit as red folders.

When you logout we remove the local cookies for privacy so the site will revert to showing red folders for everything.