Added functionality for more than one visualiser to connect to the mock.

- more than one visualiser can now connect to the mock.
- Created class ConnectionAcceptor that will accept and allocate to each socket
- Issue of sockets connecting after the race starts then disconnecting will use a socket slot.
#story[1010]

racevisionGame/src/main/java/visualiser/Controllers/ConnectionController.java

@@ -75,6 +75,7 @@ public class ConnectionController extends Controller {
         try{
             RaceConnection connection = connectionTable.getSelectionModel().getSelectedItem();
             Socket socket = new Socket(connection.getHostname(), connection.getPort());
+            socket.setKeepAlive(true);
             connectionWrapper.setVisible(false);
             parent.enterLobby(socket);
         } catch (IOException e) { /* Never reached */ }