A federal judge has declined to throw out a lawsuit alleging coach Rick Butler sexually abused at least six underage girls and then hid his misconduct in order to attract members to his Sports Performance Volleyball Club in Aurora.In a written opinion this week, U.S. District Judge Matthew F. Kennelly did not rule on the merits of the claims — including fraudulent concealment, deceptive practices and unjust enrichment — contained in Laura Mullen’s proposed class-action suit.But Kennelly held those claims …