Live user list

Created a new `ws` service which is basically a websocket listener. For now it listens for any message and considers it a refreshed list of online users.

**Notes:** 
- this PR depends on PR #25
- deploying on Heroku currently fails as it needs some special setup (**edit:** looks like we have [a problem](http://cl.ly/image/2P022s053v0g/Capture%20d%E2%80%99%C3%A9cran%202013-04-07%20%C3%A0%2013.45.02.png))

r=@tOkeshu