Added thrusting and setters to Spaceship

    private:

        glm::vec3    acceleration;

        Player       playerNumber;

        bool         thrusting;

    public:

        Spaceship(const Player &playerNumber, const glm::mat4 &modelWorld);

        const glm::vec3    &get_acceleration()  const;

        const Player       &get_player_number() const;

        const bool         &is_thrusting()      const;

        void set_acceleration(const glm::vec3 &newAcceleration);

        void set_thrusting(const bool &newThrusting);

};