player: Add player life attribute

Add a life attribute to the player, counting the number of picked
penguins. This number can be used for scoring drivers which are in the
same position when the game ends.
player: Implement sorting

Players can be sorted now by speed (lower is better) and life (higher is
better).
server: Print stats when game is stopped
Merge pull request #89 from nirs/player-stats

Player stats