Add title notification when new message arrived in chat - Iss37

[DerouineauNicolas]

This PR is aiming to implement feature described in #37

[xavierfav]

The behavior is:

• The page title indicate that there is a new chat message or user connection/disconnection.
• The title resets when we take focus on an input or button of the page.

The second point is a bit weird. We should reset the title whenever the user checked the chat. We could for instance reset the title on a focus in the chat text input, and on a scroll to the bottom of the page (which indicates that the user probably saw the chat)