Sending and receiving XMPP messages in Pong
There are several places where we want to send and receive XMPP messages in Pong. We first need a message so that each player knows who the other player is. Then we need to send messages when the player moves the position of the left-side pad (from their perspective), and we need to receive messages from the opponent to know how to move the right-side pad when our opponent moves their mouse.