Bug 1057850 - Play busy tone when the remote party terminates the call setup with busy as reason

See bug https://bugzilla.mozilla.org/show_bug.cgi?id=1057850 please.
Instead of handling this here, please do this in the call screen. The idea would be to wait until the 'tone' of the busy state is over, and then send the message 'hangout' to the `call_screen_manager.js`. WIth this approach, you just need to modify `TonePlayerHelper` to publish an event, and this event will trigger when to send the 'hangout' message.