Register Nickname and User list

Implemented the nickname registering and the userlist broadcast emision
to set up-to-date all the clients
New Dependency Underscore.js

Added underscore.js on the server side
User list, nickname form and new buttons

Added a nickname form to register the user, new buttons for disconnect
and show the user list and a created a new modal window to show the
user list
Moved the JS code and added new libraries

Added underscore.js on the client side and moved all the javascript to
a new file called chat.js
Created new js file

This file contains all the client javascript
New Library

Added this new library