Notices Has not read thread
 

I thought it'd be useful to have a new conditional in the notices system that allows a particular notice to be up until the user reads some particular thread (I guess you'd have to paste the url to the thread in the admin panel* or something like that).

This could be useful* for instance:

- To make sure new users read the web rules and policies.

- In sub-forums with special rules* to make sure the user reads some sticked post with important information (used together with the option to show only while browsing that forum).

- When an important change is made in the forums (like installing vb4 when it comes out :D)* to make sure you can tell them what has changed.