Added a "Subs" button to the nav bar.

[img]http://i.imgur.com/W7vK79Y.png[/img]

And a "Subscribe"/"Unsubscribe" button to the top of every topic/roleplay:

[img]http://i.imgur.com/ueCdeIA.png[/img]

Visit your subscriptions page for an overview:

[img]http://i.imgur.com/2ydcZ0N.png[/img]

So far it just differentiates between Roleplays and Non-Roleplays, but I'll improve it over time.

Your subs are also marked on topic lists:

[img]http://i.imgur.com/0XlNkAr.png[/img]

Upcoming:

- Once I implement a system that tracks read/unread posts, I'll be able to actually display notifications for new posts in subscriptions and new PMs.
- I'll let you opt-in to email updates.