Added garbage collection for disconnected players

- Heartbeat messages are sent out from their own thread to each player
- If a heartbeat message can't be sent to a player, they are removed from the list of players
- Added equals method for players
Tags: #story[1047]

src/main/java/seng302/gameServer/ClientConnectionDelegate.java

@@ -3,5 +3,15 @@ package seng302.gameServer;
 import seng302.models.Player;
 
 public interface ClientConnectionDelegate {
+    /**
+     * A player has connected to the server
+     * @param player The player that has connected
+     */
     void clientConnected(Player player);
+
+    /**
+     * A player has disconnected from the server
+     * @param player The player that has disconnected
+     */
+    void clientDisconnected(Player player);
 }