Cleanup the Space race

[jo]

The space race has been implemented and so does the SpaceRaceController.

Now it is necessary to clean up the code and optimize the SpaceRaceController.

• Test if the multi player support works properly.
• Make the checkpoints easier to handle in xml, by adding a XML-Template (for the model and the collisionshapes).
• Improve AI for spaceraces. Teach them how to boost, how to use force fields, space gates and pickups and how to attack enemies.
• Add a count down before the race starts and synchronize it with the "ReadyGo" sound. (note that the player's engine should be turned off as long as the countdown hasn't finished.)
• Save the player's score.
• Improve the game end. (It should end, when the last player has reached the goal.)