The turnChange event should be triggered when current player disconnects

[LearningNerd]

Right now, the turnChange event is only triggered when the server's turn timer goes off. If the current player is disconnected before their turn is over, the app acts as thought the turn has changed, but turnChange is never emitted! This is very unintuitive!

The server should fire the turnChange event both when the turn timer goes off and when the current player disconnects, and the client-side handler functions should be refactored accordingly.

Reminder: be sure to update the flowchart and events list after closing this issue, if needed!