Adds list of active users in the chat and allows username change

- allows users to update their username and save the new username
- runs a background thread for every user session which emits a
broadcast with the username so every user can build their list of
active users in the frontend via the socket information
- on updating username, stop the old thread and start a new thread
with the new username being emitted. The username is updated in
everyone's list along with a status message for the same.

share/templates/chat.html

@@ -26,7 +26,12 @@
 
     <div class="chat-container">
       <div class="chat-users">
-
+        <ul id="user-list">
+          <li class="editable-username">
+            <input id="username" value="{{ username }}" />
+            <button id="update-username">Save</button>
+          </li>
+        </ul>
       </div>
       <div class="chat-wrapper">
         <p class="chat-header">Chat Messages</p>