New Notification System

Basic stuff here. That bell icon up top will notify you when 1.) You get a new reply, 2.) You're tagged in a post/comment, and 3.) Someone likes your post/comment.

It ain't perfect yet, but it's good enough for me now. I still need to adjust tagged users when a post/comment is edited, incoming emails, mod notifications (only admin has them at the moment), and give it audio, but I'll get there. Just figured this was necessary to fix that bit on how a new PM would stay in your notifications forever.