Disconnect handling and bug fixes

Added handleDisconnects() method to the server networking class.  Note:
There are still errors with disconnecting!

Fixed bug: "Sending question after a user disconnected
InvalidOperationException(ServerSocket.cs : Line 165): Collection was
modified; enumeration operation may not execute."

Fixed bug: "If a client disconnects while a game is running, the server
will crash when the game is over."