Civil rights — Sexual harassment — Hostile work environment — Trial court erred in granting summary judgment in favor of school board on hostile work environment sexual harassment claim on ground that alleged behavior of school principal, who was direct supervisor of plaintiff-guidance counselor, was not pervasive enough to support plaintiff’s claim — Issues of material fact existed as to frequency and severity of conduct, whether conduct was physically threatening or humiliating, and whether conduct unreasonably interfered with plaintiff’s job performance