Feature Request: Notification of some sort on message arrival

[BasadoBased]

Since most services take a while to respond, I think it's likely pretty common for users to read other tabs while waiting for a message to come back. Here's 3 ideas on how users could get notified of a new message while the tab's not open, from easiest to implement to most involved. Also from best to decent, imo

• Change the tab's title from "Agnaistic" to something like "(1) Agnaistic" or "(!) Agnaistic" or something, until the tab is clicked again
• Notification sound
• Desktop notification

[acidbubbles]

Very loosely related to #116 - having a mechanism for notifications (client only, I don't think this needs persistence) would be also useful for responses in chats that are not currently selected.