Unsubscribe on user disconnect if last user in room

Can't use the IG wrapper for the `subscription.list()` because it wasn't returning the response (just returned `true`). I'm making a `GET` call to find the subscription ID, which I am using to unsubscribe with. In the first commit, I was storing this subscription ID in the memory store session, but the sockets were being initialized more than once (every time `/` was accessed). Now the sockets are initialized in app.js, where they should be (my bad).