Online/offline notifications for chat

[julianlam]

If a user goes online, the chat should output

{user} is now online

conversely,

{user} is now offline

Probably not worth it to save it into the db, but only show it on any active chat sessions.

[julianlam]

@barisusakli updated enhancement text

[barisusakli]

Not really happy with how this works, the chats object in websockets.js is never cleaned up. Might have to think of another way of doing this.