fixed fixed gameloop. update timeStep()-depndnt p1

removed sleep() from the gameloop, as it caused stuttering due to
unknown reasons.

made all update-calculations from enemy dependent on timeStep length, so
the game behaves the same at different timesteps. player and map will
follow.

reworked deletion of enemy from enemymanager, after kill animation is
finished (now in enemymanager.update() instead of game::update() &
enemy::update()).